S.D.
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
Organisations
Political parties
- Democratic Left (Italy) (2007–2010; Italian: Sinistra Democratica)
- Social Democrats (Slovenia) (founded 1993)
- Solidarity (Brazil) (founded 2012)
- Democratic Party (Poland) (founded 1937; Polish: Stronnictwo Demokratyczne)
- Sweden Democrats (founded 1988)
- Swiss Democrats, Switzerland (renamed 1990; German: Schweizer Demokraten)
- Serbian Right (founded 2018; Serbian: 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:
SD
)
Places
- Sudan (ISO 3166 country code:
SD
) - 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)
Science and technology
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)