Skip to search results Skip to filters Skip to sort Skip to selected filters

Women's Solid Slide Black Products

80 items found

Sort By

Your Selections

Search Results

. Born - Kade. Color Black. $120.00.

Brand Name: Born
Product Name: Kade
Gender: Women's
Color: Black
Price: $120.00
Rating

. Tory Burch - Jessa Toe Ring Sandals. Color Perfect Black. Low Stock. $348.00.

4 left in stock

Brand Name: Tory Burch
Product Name: Jessa Toe Ring Sandals
Gender: Women's
Color: Perfect Black
Price: $348.00
Rating

. Roxy - Slipin Slide. Color Black. $33.95.

Brand Name: Roxy
Product Name: Slipin Slide
Gender: Women's
Color: Black
Price: $33.95
Rating

Hoka - Ora Athletic Slide. Color Black. $60.00. 4.7 out of 5 stars

Brand Name: Hoka
Product Name: Ora Athletic Slide
Gender: Unisex
Color: Black
Price: $60.00
Rating: 5Rated 5 stars out of 5(21)

Vaneli - Hero. Color Black Suede. $174.95.

Brand Name: Vaneli
Product Name: Hero
Gender: Women's
Color: Black Suede
Price: $174.95
Rating

Crocs - Miami Slide Sandals. Color Metallic Black. $44.95. 3.0 out of 5 stars

Brand Name: Crocs
Product Name: Miami Slide Sandals
Gender: Women's
Color: Metallic Black
Price: $44.95
Rating: 3Rated 3 stars out of 5(12)

Reef - Reef Solana Leather. Color Dusty Black. $59.95.

Brand Name: Reef
Product Name: Reef Solana Leather
Gender: Women's
Color: Dusty Black
Price: $59.95
Rating

Dolce Vita - Darsey. Color Onyx. $99.95.

Brand Name: Dolce Vita
Product Name: Darsey
Gender: Women's
Color: Onyx
Price: $99.95
Rating

MICHAEL Michael Kors - Saylor Slide. Color Black1. On sale for $130.50. MSRP $145.00..

Brand Name: MICHAEL Michael Kors
Product Name: Saylor Slide
Gender: Women's
Color: Black1
Price: $130.50MSRP: $145.00
Rating

Dolce Vita - Wesla Stud. Color Black. $113.90. 4.0 out of 5 stars

Brand Name: Dolce Vita
Product Name: Wesla Stud
Gender: Women's
Color: Black
Price: $113.90
Rating: 4Rated 4 stars out of 5(1)

Crocs - Brooklyn Luxe Sandal. Color Black/Black. On sale for $58.46. MSRP $74.95.. 3.4 out of 5 stars

Brand Name: Crocs
Product Name: Brooklyn Luxe Sandal
Gender: Women's
Color: Black/Black
Price: $58.46MSRP: $74.95
Rating: 3Rated 3 stars out of 5(8)

AllSaints - Ellie Stud Slider. Color Black. Low Stock. $199.00. 1.5 out of 5 stars

4 left in stock

Brand Name: AllSaints
Product Name: Ellie Stud Slider
Gender: Women's
Color: Black
Price: $199.00
Rating: 2Rated 2 stars out of 5(2)

FitFlop - Iqushion Leather Toe-Post Sandals. Color Black. On sale for $66.50. MSRP $95.00.. 4.0 out of 5 stars

Black FitFlop Iqushion Leather Toe-Post Sandals

Brand Name: FitFlop
Product Name: Iqushion Leather Toe-Post Sandals
Gender: Women's
Color: Black
Price: $66.50MSRP: $95.00
Rating: 4Rated 4 stars out of 5(1)

Sofft - Noella. Color Black. $109.95. 3.3 out of 5 stars

Brand Name: Sofft
Product Name: Noella
Gender: Women's
Color: Black
Price: $109.95
Rating: 3Rated 3 stars out of 5(3)

Aerosoles - Brady. Color Black Leather. On sale for $47.17. MSRP $89.00.. 4.0 out of 5 stars

Brand Name: Aerosoles
Product Name: Brady
Gender: Women's
Color: Black Leather
Price: $47.17MSRP: $89.00
Rating: 4Rated 4 stars out of 5(1)

Sofft - Noble. Color Black. $109.95. 3.3 out of 5 stars

Brand Name: Sofft
Product Name: Noble
Gender: Women's
Color: Black
Price: $109.95
Rating: 3Rated 3 stars out of 5(9)

Naturalizer - Inez2 Slides. Color Black Fabric. On sale for $85.00. MSRP $125.00.. 2.5 out of 5 stars

Brand Name: Naturalizer
Product Name: Inez2 Slides
Gender: Women's
Color: Black Fabric
Price: $85.00MSRP: $125.00
Rating: 3Rated 3 stars out of 5(4)

Dolce Vita - Aisha. Color Black. On sale for $99.99. MSRP $120.00.. 3.0 out of 5 stars

Brand Name: Dolce Vita
Product Name: Aisha
Gender: Women's
Color: Black
Price: $99.99MSRP: $120.00
Rating: 3Rated 3 stars out of 5(1)

DV Dolce Vita - Hobbs. Color Black. On sale for $46.02. MSRP $59.00.. 3.0 out of 5 stars

Brand Name: DV Dolce Vita
Product Name: Hobbs
Gender: Women's
Color: Black
Price: $46.02MSRP: $59.00
Rating: 3Rated 3 stars out of 5(2)

Paul Green - Tiki Slide. Color Black Leather. On sale for $314.88. MSRP $384.00.. 1.0 out of 5 stars

Brand Name: Paul Green
Product Name: Tiki Slide
Gender: Women's
Color: Black Leather
Price: $314.88MSRP: $384.00
Rating: 1Rated 1 star out of 5(1)

Hey Dude - Delray Slide Classic. Color Black/Black. On sale for $45.10. MSRP $59.99.. 4.5 out of 5 stars

Brand Name: Hey Dude
Product Name: Delray Slide Classic
Gender: Women's
Color: Black/Black
Price: $45.10MSRP: $59.99
Rating: 4Rated 4 stars out of 5(75)

Hey Dude - Delray Slide Mono. Color Black/Black. On sale for $45.17. MSRP $59.99.. 4.4 out of 5 stars

Brand Name: Hey Dude
Product Name: Delray Slide Mono
Gender: Women's
Color: Black/Black
Price: $45.17MSRP: $59.99
Rating: 4Rated 4 stars out of 5(32)

Comfortiva - Gervaise. Color Black. On sale for $72.96. MSRP $99.95.. 3.4 out of 5 stars

Brand Name: Comfortiva
Product Name: Gervaise
Gender: Women's
Color: Black
Price: $72.96MSRP: $99.95
Rating: 3Rated 3 stars out of 5(5)

Madewell - Greene Thong Slide. Color True Black. Low Stock. $68.00.

2 left in stock

Brand Name: Madewell
Product Name: Greene Thong Slide
Gender: Women's
Color: True Black
Price: $68.00
Rating

Chinese Laundry - Clarke. Color Black. Low Stock. $69.95. 2.5 out of 5 stars

7 left in stock

Brand Name: Chinese Laundry
Product Name: Clarke
Gender: Women's
Color: Black
Price: $69.95
Rating: 3Rated 3 stars out of 5(2)

Marc Fisher LTD - Hattie. Color Black Leather. On sale for $69.99. MSRP $140.00.. 3.0 out of 5 stars

Brand Name: Marc Fisher LTD
Product Name: Hattie
Gender: Women's
Color: Black Leather
Price: $69.99MSRP: $140.00
Rating: 3Rated 3 stars out of 5(1)

Sofft - Fallon. Color Black. $119.95. 4.3 out of 5 stars

Brand Name: Sofft
Product Name: Fallon
Gender: Women's
Color: Black
Price: $119.95
Rating: 4Rated 4 stars out of 5(7)

MICHAEL Michael Kors - Elena Flat Slide. Color Black. On sale for $96.25. MSRP $125.00..

Black MICHAEL Michael Kors Elena Flat Slide

Brand Name: MICHAEL Michael Kors
Product Name: Elena Flat Slide
Gender: Women's
Color: Black
Price: $96.25MSRP: $125.00
Rating

Donald Pliner - Seena. Color Black. Low Stock. On sale for $94.80. MSRP $158.00.. 3.0 out of 5 stars

8 left in stock

Brand Name: Donald Pliner
Product Name: Seena
Gender: Women's
Color: Black
Price: $94.80MSRP: $158.00
Rating: 3Rated 3 stars out of 5(2)

SoftWalk - Jenna. Color Black. On sale for $92.36. MSRP $119.95.. 3.0 out of 5 stars

Brand Name: SoftWalk
Product Name: Jenna
Gender: Women's
Color: Black
Price: $92.36MSRP: $119.95
Rating: 3Rated 3 stars out of 5(4)

. Crocs - Stomp Slide. Color Black. On sale for $39.98. MSRP $59.95.. 3.6 out of 5 stars

Brand Name: Crocs
Product Name: Stomp Slide
Gender: Unisex
Color: Black
Price: $39.98MSRP: $59.95
Rating: 4Rated 4 stars out of 5(36)

DV Dolce Vita - Liliah. Color Black. On sale for $46.22. MSRP $59.00.. 1.0 out of 5 stars

Brand Name: DV Dolce Vita
Product Name: Liliah
Gender: Women's
Color: Black
Price: $46.22MSRP: $59.00
Rating: 1Rated 1 star out of 5(1)

Seychelles - Chai. Color Black. Low Stock. $98.95.

1 left in stock

Brand Name: Seychelles
Product Name: Chai
Gender: Women's
Color: Black
Price: $98.95
Rating

Nisolo - Ella Go-To Flatform Slide. Color Black. Low Stock. $137.99. 3.3 out of 5 stars

7 left in stock

Brand Name: Nisolo
Product Name: Ella Go-To Flatform Slide
Gender: Women's
Color: Black
Price: $137.99
Rating: 3Rated 3 stars out of 5(3)

Bernardo - Charleston. Color Black. Low Stock. On sale for $118.99. MSRP $288.00.. 4.5 out of 5 stars

5 left in stock

Brand Name: Bernardo
Product Name: Charleston
Gender: Women's
Color: Black
Price: $118.99MSRP: $288.00
Rating: 5Rated 5 stars out of 5(2)

SKECHERS Performance - GO Recover Refresh Arch Fit Slide. Color Black/Black. On sale for $46.77. MSRP $60.00.. 4.0 out of 5 stars

Black SKECHERS Performance GO Recover Refresh Arch Fit Slide

Brand Name: SKECHERS Performance
Product Name: GO Recover Refresh Arch Fit Slide
Gender: Women's
Color: Black/Black
Price: $46.77MSRP: $60.00
Rating: 4Rated 4 stars out of 5(11)

Marc Joseph New York - Walcott Ave. Color Black Napa. On sale for $116.25. MSRP $155.00..

Brand Name: Marc Joseph New York
Product Name: Walcott Ave
Gender: Women's
Color: Black Napa
Price: $116.25MSRP: $155.00
Rating

L.L.Bean - Go Anywhere Strap Sandal Leather. Color Black. Low Stock. On sale for $60.52. MSRP $89.00.. 5.0 out of 5 stars

4 left in stock

Black L.L.Bean Go Anywhere Strap Sandal Leather

Brand Name: L.L.Bean
Product Name: Go Anywhere Strap Sandal Leather
Gender: Women's
Color: Black
Price: $60.52MSRP: $89.00
Rating: 5Rated 5 stars out of 5(1)

Dansko - Justine. Color Black Calf. $119.95. 4.5 out of 5 stars

Brand Name: Dansko
Product Name: Justine
Gender: Women's
Color: Black Calf
Price: $119.95
Rating: 5Rated 5 stars out of 5(8)

MICHAEL Michael Kors - Corrine Platform. Color Black. On sale for $98.58. MSRP $145.00.. 5.0 out of 5 stars

Black MICHAEL Michael Kors Corrine Platform

Brand Name: MICHAEL Michael Kors
Product Name: Corrine Platform
Gender: Women's
Color: Black
Price: $98.58MSRP: $145.00
Rating: 5Rated 5 stars out of 5(1)

ALDO - Faiza. Color Black. On sale for $68.53. MSRP $75.00..

Brand Name: ALDO
Product Name: Faiza
Gender: Women's
Color: Black
Price: $68.53MSRP: $75.00
Rating

ECCO - Cozmo 2 Band Platform. Color Black. Low Stock. On sale for $112.46. MSRP $150.00.. 3.7 out of 5 stars

8 left in stock

Brand Name: ECCO
Product Name: Cozmo 2 Band Platform
Gender: Women's
Color: Black
Price: $112.46MSRP: $150.00
Rating: 4Rated 4 stars out of 5(3)

MICHAEL Michael Kors - Zaza Flip Flop. Color Black. Low Stock. $65.00.

1 left in stock

Black MICHAEL Michael Kors Zaza Flip Flop

Brand Name: MICHAEL Michael Kors
Product Name: Zaza Flip Flop
Gender: Women's
Color: Black
Price: $65.00
Rating

Clarks - Arla Wave. Color Black Textile. $64.95. 4.0 out of 5 stars

Brand Name: Clarks
Product Name: Arla Wave
Gender: Women's
Color: Black Textile
Price: $64.95
Rating: 4Rated 4 stars out of 5(14)

PIKOLINOS - Mahon W9E-0821. Color Black. On sale for $130.90. MSRP $170.00.. 4.0 out of 5 stars

Brand Name: PIKOLINOS
Product Name: Mahon W9E-0821
Gender: Women's
Color: Black
Price: $130.90MSRP: $170.00
Rating: 4Rated 4 stars out of 5(1)

SKECHERS - Easy Going - Sundown. Color Black/Black. On sale for $44.95. MSRP $49.99.. 3.7 out of 5 stars

Brand Name: SKECHERS
Product Name: Easy Going - Sundown
Gender: Women's
Color: Black/Black
Price: $44.95MSRP: $49.99
Rating: 4Rated 4 stars out of 5(9)

Bueno - Turner Perf. Color Black. Low Stock. On sale for $71.99. MSRP $110.00..

3 left in stock

Brand Name: Bueno
Product Name: Turner Perf
Gender: Women's
Color: Black
Price: $71.99MSRP: $110.00
Rating

Clarks - Reileigh Bay. Color Black Leather. On sale for $65.07. MSRP $90.00.. 3.5 out of 5 stars

Brand Name: Clarks
Product Name: Reileigh Bay
Gender: Women's
Color: Black Leather
Price: $65.07MSRP: $90.00
Rating: 4Rated 4 stars out of 5(4)

Schutz - Lolita Mule. Color Black. Low Stock. $98.00.

1 left in stock

Brand Name: Schutz
Product Name: Lolita Mule
Gender: Women's
Color: Black
Price: $98.00
Rating

Schutz - Enola Crossed. Color Black. Low Stock. $138.00.

6 left in stock

Brand Name: Schutz
Product Name: Enola Crossed
Gender: Women's
Color: Black
Price: $138.00
Rating

Stuart Weitzman - Nudistia Espadrille Wedge. Color Black. On sale for $262.50. MSRP $350.00..

Black Stuart Weitzman Nudistia Espadrille Wedge

Brand Name: Stuart Weitzman
Product Name: Nudistia Espadrille Wedge
Gender: Women's
Color: Black
Price: $262.50MSRP: $350.00
Rating

Johnston & Murphy - Lilly Chain Slide. Color Black. Low Stock. On sale for $82.80. MSRP $138.00.. 3.0 out of 5 stars

9 left in stock

Black Johnston & Murphy Lilly Chain Slide

Brand Name: Johnston & Murphy
Product Name: Lilly Chain Slide
Gender: Women's
Color: Black
Price: $82.80MSRP: $138.00
Rating: 3Rated 3 stars out of 5(1)

Seychelles - End Of Time. Color Black. On sale for $104.47. MSRP $109.00.. 4.0 out of 5 stars

Brand Name: Seychelles
Product Name: End Of Time
Gender: Women's
Color: Black
Price: $104.47MSRP: $109.00
Rating: 4Rated 4 stars out of 5(4)

Merrell - Terran 4 Slide. Color Black. $89.95. 3.4 out of 5 stars

Brand Name: Merrell
Product Name: Terran 4 Slide
Gender: Women's
Color: Black
Price: $89.95
Rating: 3Rated 3 stars out of 5(10)

Blue by Betsey Johnson - Anny. Color Black. On sale for $98.54. MSRP $119.00..

Brand Name: Blue by Betsey Johnson
Product Name: Anny
Gender: Women's
Color: Black
Price: $98.54MSRP: $119.00
Rating

LAUREN Ralph Lauren - Sasha Sandal. Color Black/Black. Low Stock. On sale for $166.20. MSRP $175.00.. 3.8 out of 5 stars

2 left in stock

Brand Name: LAUREN Ralph Lauren
Product Name: Sasha Sandal
Gender: Women's
Color: Black/Black
Price: $166.20MSRP: $175.00
Rating: 4Rated 4 stars out of 5(4)

Hey Dude - Collins Sandal Mono Sport. Color Black/Black. On sale for $48.05. MSRP $59.99.. 4.5 out of 5 stars

Black Hey Dude Collins Sandal Mono Sport

Brand Name: Hey Dude
Product Name: Collins Sandal Mono Sport
Gender: Women's
Color: Black/Black
Price: $48.05MSRP: $59.99
Rating: 5Rated 5 stars out of 5(42)

Chaco - Townes Slide. Color Black 1. On sale for $79.99. MSRP $100.00.. 2.7 out of 5 stars

Brand Name: Chaco
Product Name: Townes Slide
Gender: Women's
Color: Black 1
Price: $79.99MSRP: $100.00
Rating: 3Rated 3 stars out of 5(3)

SKECHERS - Easy Going - Slide On By. Color Black/Black. On sale for $44.95. MSRP $49.99.. 4.2 out of 5 stars

Brand Name: SKECHERS
Product Name: Easy Going - Slide On By
Gender: Women's
Color: Black/Black
Price: $44.95MSRP: $49.99
Rating: 4Rated 4 stars out of 5(5)

SKECHERS - Arch Fit - New Beginning. Color Black/Black. Low Stock. On sale for $40.00. MSRP $56.99.. 4.5 out of 5 stars

2 left in stock

Brand Name: SKECHERS
Product Name: Arch Fit - New Beginning
Gender: Women's
Color: Black/Black
Price: $40.00MSRP: $56.99
Rating: 5Rated 5 stars out of 5(4)

SKECHERS - Rumble On - Glammed Up. Color Black/Black. Low Stock. $49.99. 4.2 out of 5 stars

1 left in stock

Brand Name: SKECHERS
Product Name: Rumble On - Glammed Up
Gender: Women's
Color: Black/Black
Price: $49.99
Rating: 4Rated 4 stars out of 5(4)

Stuart Weitzman - Carmen 75 Slide. Color Black. On sale for $332.50. MSRP $475.00..

Brand Name: Stuart Weitzman
Product Name: Carmen 75 Slide
Gender: Women's
Color: Black
Price: $332.50MSRP: $475.00
Rating

UGG - Goldenstar Hi Slide. Color Black. $139.95. 4.5 out of 5 stars

Brand Name: UGG
Product Name: Goldenstar Hi Slide
Gender: Women's
Color: Black
Price: $139.95
Rating: 4Rated 4 stars out of 5(95)

SOREL - Joanie™ Heel Slide. Color Black/Black. On sale for $101.25. MSRP $135.00.. 4.5 out of 5 stars

Brand Name: SOREL
Product Name: Joanie™ Heel Slide
Gender: Women's
Color: Black/Black
Price: $101.25MSRP: $135.00
Rating: 4Rated 4 stars out of 5(13)

SOREL - Ella™ III Slide. Color Black/Black. On sale for $50.92. MSRP $85.00.. 4.6 out of 5 stars

Brand Name: SOREL
Product Name: Ella™ III Slide
Gender: Women's
Color: Black/Black
Price: $50.92MSRP: $85.00
Rating: 5Rated 5 stars out of 5(8)

MICHAEL Michael Kors - Colby Slide. Color Black. Low Stock. On sale for $74.80. MSRP $145.00.. 5.0 out of 5 stars

9 left in stock

Brand Name: MICHAEL Michael Kors
Product Name: Colby Slide
Gender: Women's
Color: Black
Price: $74.80MSRP: $145.00
Rating: 5Rated 5 stars out of 5(1)

Reef - Cushion Bondi Bay. Color Black/Black. $59.96. 3.0 out of 5 stars

Brand Name: Reef
Product Name: Cushion Bondi Bay
Gender: Women's
Color: Black/Black
Price: $59.96
Rating: 3Rated 3 stars out of 5(1)

Reef - Cushion Bondi 2 Bar. Color Black/Black. $59.95. 3.7 out of 5 stars

Brand Name: Reef
Product Name: Cushion Bondi 2 Bar
Gender: Women's
Color: Black/Black
Price: $59.95
Rating: 4Rated 4 stars out of 5(3)

Sam Edelman - Linnie Fray. Color Black. On sale for $97.90. MSRP $140.00.. 4.5 out of 5 stars

Brand Name: Sam Edelman
Product Name: Linnie Fray
Gender: Women's
Color: Black
Price: $97.90MSRP: $140.00
Rating: 5Rated 5 stars out of 5(2)

Sam Edelman - Julia. Color Black. On sale for $56.00. MSRP $140.00.. 3.0 out of 5 stars

Brand Name: Sam Edelman
Product Name: Julia
Gender: Women's
Color: Black
Price: $56.00MSRP: $140.00
Rating: 3Rated 3 stars out of 5(2)

COACH - Florence Sandal. Color Black. $125.00. 3.5 out of 5 stars

Brand Name: COACH
Product Name: Florence Sandal
Gender: Women's
Color: Black
Price: $125.00
Rating: 4Rated 4 stars out of 5(2)

Crocs - Brooklyn Slide. Color Black. On sale for $42.43. MSRP $54.95.. 3.8 out of 5 stars

Brand Name: Crocs
Product Name: Brooklyn Slide
Gender: Women's
Color: Black
Price: $42.43MSRP: $54.95
Rating: 4Rated 4 stars out of 5(60)

Vince - Pia-2. Color Black. Low Stock. On sale for $262.50. MSRP $350.00..

5 left in stock

Brand Name: Vince
Product Name: Pia-2
Gender: Women's
Color: Black
Price: $262.50MSRP: $350.00
Rating

FitFlop - Chrissie II Haus Crochet-Stitch Shearling Slippers. Color All Black. On sale for $69.94. MSRP $120.00.. 2.0 out of 5 stars

Black FitFlop Chrissie II Haus Crochet-Stitch Shearling Slippers

Brand Name: FitFlop
Product Name: Chrissie II Haus Crochet-Stitch Shearling Slippers
Gender: Women's
Color: All Black
Price: $69.94MSRP: $120.00
Rating: 2Rated 2 stars out of 5(1)

ALDO - Valabenna. Color Black. On sale for $72.00. MSRP $90.00..

Brand Name: ALDO
Product Name: Valabenna
Gender: Women's
Color: Black
Price: $72.00MSRP: $90.00
Rating

Madden Girl - Windy. Color Black Paris. Low Stock. On sale for $48.60. MSRP $54.00.. 3.0 out of 5 stars

1 left in stock

Brand Name: Madden Girl
Product Name: Windy
Gender: Women's
Color: Black Paris
Price: $48.60MSRP: $54.00
Rating: 3Rated 3 stars out of 5(2)

SLAYE - Matilda. Color Black. Low Stock. On sale for $71.77. MSRP $159.50.. 4.0 out of 5 stars

3 left in stock

Brand Name: SLAYE
Product Name: Matilda
Gender: Women's
Color: Black
Price: $71.77MSRP: $159.50
Rating: 4Rated 4 stars out of 5(2)

Seychelles - Heartfelt. Color Black Leather. Low Stock. $108.95. 1.5 out of 5 stars

1 left in stock

Brand Name: Seychelles
Product Name: Heartfelt
Gender: Women's
Color: Black Leather
Price: $108.95
Rating: 2Rated 2 stars out of 5(2)

Tory Burch - Bubble Jelly. Color Perfect Black/Perfect Black. On sale for $99.00. MSRP $188.00.. 3.5 out of 5 stars

Brand Name: Tory Burch
Product Name: Bubble Jelly
Gender: Women's
Color: Perfect Black/Perfect Black
Price: $99.00MSRP: $188.00
Rating: 3Rated 3 stars out of 5(37)

Madden Girl - Shelbie. Color Black Fabric. Low Stock. On sale for $46.06. MSRP $49.00.. 3.0 out of 5 stars

1 left in stock

Brand Name: Madden Girl
Product Name: Shelbie
Gender: Women's
Color: Black Fabric
Price: $46.06MSRP: $49.00
Rating: 3Rated 3 stars out of 5(3)

Women's Solid Slide Black Products

Your Selections

Search Results

Get on the List

About Zappos

Customer Service

Resources

Explore Zappos