A day is a unit of temporal measurement for a literal day or epoch of time.

Day, DAY or Days may also refer to:

• Daytime
• Awareness day, a date set by a major organisation or government to commemorate a cause of importance on a national or international level
• Synodic day, the time for any given celestial body to complete a rotation

• Day (surname)
• Days (surname)
• Day9, alias of Sean Plott, former professional gamer and e-sports commentator
• John Day Smith (1845–1933), American lawyer, judge, and politician

• Day, an 1881 painting by William-Adolphe Bouguereau
• Day (Michelangelo), a sculpture in the Medici Chapels in Florence, Italy

• Days (2020 film), a Taiwanese drama film directed by Tsai Ming-liang
• Days (2023 film), a Canadian documentary film directed by Geneviève Dulude-De Celles
• Days of Heaven, a 1978 American romantic period drama film

• Days of Our Lives, an American soap opera
• "Day" (The Acolyte), an episode of The Acolyte

• Day (Wiesel novel), a 1962 novel by Elie Wiesel
• Day (Kennedy novel), a 2007 novel by A. L. Kennedy
• "Days" (poem), a short poem by Philip Larkin
• Days (manga), a manga series by Tsuyoshi Yasuda

• DJ Day, American DJ, producer, and musician

• Days (album), by Real Estate, 2011
• Days, by Tim Knol, 2011
• Day, an EP by Jeong Se-woon, 2019

• "Days" (Alisa Mizuki song), 1997
• "Days" (Flow song), 2005
• "Days" (High and Mighty Color song), 2005
• "Days" (The Kinks song), 1968; covered by Kirsty MacColl, 1989
• "Days", a 1972 song by Steve Peregrin Took from the 1995 posthumous album The Missing Link To Tyrannosaurus Rex
• "Days"/"Green", by Ayumi Hamasaki, 2008
• "Day", by Katatonia from Brave Murder Day
• "Days", by David Bowie from Reality
• "Days", by the Drums from Portamento

• Day, California, an unincorporated community
• Day, Florida, a census-designated place
• Day, Minnesota, an unincorporated community
• Day, Missouri, an unincorporated community
• Day, New York, a town
• Day, Wisconsin, a town
• Day County, South Dakota
• Day Township, Michigan
• Dayton International Airport, (IATA: DAY), Dayton, Ohio's main airport
• Days Canyon, a valley in Utah

• Le Day [fr], a hamlet in the municipality of Vallorbe, Vaud canton, Switzerland

• Day (automobile), an automobile built in Detroit, Michigan, from 1911 to 1914
• John Day Company, an American publisher
• Day Software, an American/Swiss content management system vendor

• Day language, a Mbum-Day language of southern Chad

• The Day (disambiguation)
• The Days (disambiguation)
• Day-Lewis, a surname
• Daye (disambiguation)
• Dayes, a surname
• Justice Day (disambiguation)
• Mars sol, a "day" on the planet Mars
• WDAY (disambiguation), media companies with the call letters DAY