SD

SD may refer to:

Military and weaponry

 * Smith & Wesson SD, a line of pistol (first made 2010)
 * SD radar, an early US Navy radar system
 * Southern Cross Decoration (SD), a South African military award

Political parties

 * Democratic Left (Italy) (2007–2010; Sinistra Democratica)
 * Social Democrats (Slovenia) (founded 1993)
 * Solidarity (Brazil) (founded 2012)
 * Democratic Party (Poland) (founded 1937; Stronnictwo Demokratyczne)
 * Sweden Democrats (founded 1988)
 * Swiss Democrats, Switzerland (renamed 1990; Schweizer Demokraten)
 * Serbian Right (founded 2018; Srpska desnica)

Other organisations

 * Sicherheitsdienst, Nazi intelligence service (1931–1945)
 * Sisters of the Destitute, a Syro-Malabar Catholic order (founded 1927)
 * Sudan Airways (founded 1946; IATA: )

Places

 * Sudan (ISO 3166 country code: )
 * A common abbreviation for the U.S. city of San Diego, California and the San Diego Padres—the city's Major League Baseball team
 * Shandong, a province of China
 * South Dakota, a US state
 * Eswatini (formerly Swaziland; SD on vehicle plates)

Astronomy

 * Subdwarf, a class of star
 * Surface detector, of cosmic rays at the Pierre Auger Observatory

Electronics and computing

 * SD card (Secure Digital), a flash memory card format
 * Software Distributor, an HP-UX system
 * Standard-definition television
 * Super Density Disc, an optical disc format
 * Stable Diffusion, a text-to-image generator

Mathematics

 * sd (elliptic function), one of Jacobi's elliptic functions
 * Standard deviation (SD), a statistical measure of variation

Medicine

 * Spasmodic dysphonia, a voice disorder
 * Stable disease, a RECIST chemotherapy outcome

Other uses in science and technology

 * Service design, holistic design of service experience
 * Spiral Dynamics, a model of individual and societal development
 * Storm Data, a US meteorological journal
 * System dynamics, of nonlinear systems

Other uses

 * Sekolah Dasar, term for primary school in Indonesia
 * Super D (cycling), a class of mountain bike race
 * Super deformed, an art style
 * Sindhi language (ISO 639-1 code: sd)
 * sine die, Latin, undated (literally without a day)