S is the nineteenth letter of the English alphabet.

S may also refer to:

• s, seconds, in an amount of time

• Long s (ſ), a form of the lower-case letter s formerly used where "s" occurred in the middle or at the beginning of a word
• s, the International Phonetic Alphabet symbol for a voiceless alveolar sibilant sound
• S, the subject of an intransitive verb
• Ѕ, the Cyrillic letter Dze
• Տ, the Armenian letter tyun
• Ⴝ, the Georgian Asomtavruli letter ch'ari

• South, a cardinal direction, usually shown at the bottom of a map or compass
• S postcode area, England, centered around Sheffield
• S, the designation letter for Sierra Time Zone, the military time zone for UTC−06:00

• S (New York City Subway service), one of the three services:
  • Franklin Avenue Shuttle
  • 42nd Street Shuttle (also called the Grand Central/Times Square Shuttle) (internally referred to as the 0)
  • Rockaway Park Shuttle (also called Rockaway Shuttle) (internally referred to as the H)
• Toei Shinjuku Line, a subway service operated by the Tokyo Metropolitan Bureau of Transportation (Toei), labeled
• Sennichimae Line, a subway service operated by the Osaka Metro, labeled
• , the official West Japan Railway Company service symbol for the Kansai Airport Line
• Shrirangapattana railway station (Indian Railways station code: S), Karnataka, India
• Karjat railway station (Mumbai Suburban Railway station code: S), Maharastra, India

• Bojonegoro, Mojokerto, Tuban, Lamongan and Jombang (vehicle registration prefix S)

• Aion S, a Chinese electric compact executive sedan
• Jaguar S-Type (1963), a British sports saloon
• Jaguar S-Type (1999), a British executive saloon
• Mercedes-Benz S-Class, a German full-size luxury car series
• Mini Cooper S, a British hot hatch
• Neta S, a Chinese electric sedan
• Tesla Model S, an American electric executive sedan

• Sony Vision-S, a Japanese mid-size electric concept sedan

• Acura Type-S, a range of Japanese performance vehicles
• Audi S, a range of German performance vehicles
• Honda S series, series of Japanese sports cars
• Jaguar S, a range of British performance vehicles
• Saviem S, a range of French medium-duty cab-over trucks

• Integral symbol (∫), used in mathematics to denote integrals and antiderivatives
• S combinator in combinatory logic
• Sphere
• S (set theory), an axiomatic set theory
• s(n), the aliquot sum of an integer n

• Sulfur, symbol S, a chemical element
• S, the symbol for entropy
• S, a non-SI unit used to designate molecule size named after the Svedberg sedimentation coefficient
• (S), a label that denotes one of two chiral center configurations in the R/S system
• s, one of the Mandelstam variables, the square of the invariant mass
• Siemens (unit), the SI derived unit of electric conductance
• S-block of the periodic table, which includes alkali metals, alkaline earth metals, and hydrogen and helium
• Spin (physics)
• s, an abbreviation for solid
• S-matrix for how a particle physics system works under a scattering process. This is a distinct concept from scattering parameters, below, which may also be referred to as an S-matrix in the context of radio frequency transmissions.
• Scattering parameters as S-matrix or S-parameters for how an electrical network behaves at some frequency, used e.g. with radio transmission
• S band, a band of radio which ranges from 2 to 4 GHz

• Serine, a standard amino acid abbreviated as Ser or S
• ATC code S Sensory organs, a section of the Anatomical Therapeutic Chemical Classification System
• S phase or synthesis phase, a period in the cell cycle during interphase

• Nikon S-mount, type of interchangeable lens mount used by a series of Nikon 35 mm rangefinder cameras
• Nikon S, a 34 mm rangefinder film camera
• Nikon Pronea S, an APS film camera made by Nikon
• Samsung Galaxy S (2010 smartphone), the first flagship smartphone of the Samsung Galaxy S series
• S (programming language), an environment for statistical computing and graphics
• <s>, the opening tag for the HTML element denoting information that is "no longer accurate or no longer relevant", usually rendered as strike-through text
• S record or SREC, a file format with an ASCII representation of Binary data

• S, the pen name of Percy Bysshe Shelley
• "S.", the nickname for Solomon Shereshevsky (1886-1958), a Russian journalist, mnemonist, and synesthete notable for his unusual memory abilities

• S. (Dorst novel), written by Doug Dorst based on story by J.J. Abrams
• S. (Updike novel), part of The Scarlet Letter trilogy
• S (novel series), a 2005-2006 light novel series

• S, the stage name of singer-songwriter and guitarist Jenn Champion
• S (group), a short-lived South Korean music group active in 2003 and 2014
• S, a 2001 EP by Japanese musical duo NaNa
• S (EP), a 2013 EP by American singer SZA
• Numbering of Franz Liszt's works according to Humphrey Searle's catalogue
• "S" (song), by Japanese band Sid

• S, the production code for the 1965 Doctor Who serial The Time Meddler

• S, the protagonist of Heavy Liquid

• Safety (gridiron football position), a player role in American and Canadian football, a kind of defensive back
• Strike (baseball), when the ball passes through the batter's strike zone

• s, shilling (British coin), a denomination of sterling coinage worth 0.05 £, or, pre-decimal, 12 d
• S, old Israeli shekel, used 1980–1985

• S by Shakira, the first woman's fragrance by Colombian singer songwriter Shakira
• A party label for the Swedish Social Democratic Party
• Cool S, a graffiti sign
• S, the prefix before a "Sawyer number" denoting an entry in Anglo-Saxon Charters: an Annotated List and Bibliography

• 's (disambiguation)
• -s (disambiguation)
• S class (disambiguation)
• S Curve (disambiguation)
• Split S