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 The Southern Cross Decoration, post-nominal letters SD, is a South African military decoration for merit which was instituted by the Republic on 1 July 1975. It was awarded to officers of the South African Defence Force for outstanding service ...

(SD), a South African military award

Organisations

Political parties

Democratic Left (Italy) Democratic Left (, SD), whose complete name was Democratic Left. For European Socialism (''Sinistra Democratica. Per il Socialismo Europeo''), was a democratic-socialist political party in Italy. SD was founded on 5 May 2007 by splinters of ...

(2007–2010; ) *

Social Democrats (Slovenia) The Social Democrats (, SD) is a centre-left social democratic political party in Slovenia. Led by Matjaž Han, the party was known as the United List of Social Democrats ( ) from 1993 until 2005. It is the successor of the League of Communists ...

(founded 1993) *

Solidarity (Brazil) Solidarity ( Portuguese: ''Solidariedade'', ) is a Brazilian social-democratic Social democracy is a social, economic, and political philosophy within socialism that supports political and economic democracy and a gradualist, reformist, a ...

(founded 2012) * Democratic Party (Poland) (founded 1937; ) *

Sweden Democrats The Sweden Democrats ( , SD ) is a Nationalism, nationalist and Right-wing populism, right-wing populist political party in Sweden founded in 1988. As of 2024, it is the largest member of Sweden's Right-wing politics, right-wing bloc and the sec ...

(founded 1988) * Swiss Democrats, Switzerland (renamed 1990; ) *

Serbian Right The Serbian Right (, abbr. SD) is a far-right political party in Serbia. The party was founded in 2018 by Miša Vacić. The party has been accused of being a satellite of the ruling Serbian Progressive Party (SNS). History Serbian Right was ...

(founded 2018; )

Other organisations

* ''

Sicherheitsdienst ' (, "Security Service"), full title ' ("Security Service of the ''Reichsführer-SS''"), or SD, was the intelligence agency of the Schutzstaffel, SS and the Nazi Party in Nazi Germany. Established in 1931, the SD was the first Nazi intelligence ...

'', Nazi intelligence service (1931–1945) * Sisters of the Destitute, a Syro-Malabar Catholic order (founded 1927) *

Sudan Airways Sudan Airways () is the national airline of Sudan, headquartered in Khartoum. Since 2012, the company has been fully owned by the Government of Sudan. One of the oldest African Air carrier, carriers, it was formed in and started scheduled oper ...

(founded 1946; IATA:SD)

Places

Sudan Sudan, officially the Republic of the Sudan, is a country in Northeast Africa. It borders the Central African Republic to the southwest, Chad to the west, Libya to the northwest, Egypt to the north, the Red Sea to the east, Eritrea and Ethiopi ...

(ISO 3166 country code:SD) * A common abbreviation for the U.S. city of

San Diego, California San Diego ( , ) is a city on the Pacific coast of Southern California, adjacent to the Mexico–United States border. With a population of over 1.4 million, it is the List of United States cities by population, eighth-most populous city in t ...

and the

San Diego Padres The San Diego Padres are an American professional baseball team based in San Diego. The Padres compete in Major League Baseball (MLB) as a member club of the National League (baseball), National League (NL) National League West, West Division. ...

—the city's

Major League Baseball Major League Baseball (MLB) is a professional baseball league composed of 30 teams, divided equally between the National League (baseball), National League (NL) and the American League (AL), with 29 in the United States and 1 in Canada. MLB i ...

team *

Shandong Shandong is a coastal Provinces of China, province in East China. Shandong has played a major role in Chinese history since the beginning of Chinese civilization along the lower reaches of the Yellow River. It has served as a pivotal cultural ...

, a province of China *

South Dakota South Dakota (; Sioux language, Sioux: , ) is a U.S. state, state in the West North Central states, North Central region of the United States. It is also part of the Great Plains. South Dakota is named after the Dakota people, Dakota Sioux ...

, a US state *

Eswatini Eswatini, formally the Kingdom of Eswatini, also known by its former official names Swaziland and the Kingdom of Swaziland, is a landlocked country in Southern Africa. It is bordered by South Africa on all sides except the northeast, where i ...

(formerly ''Swaziland''; ''SD'' on vehicle plates)

Science and technology

Astronomy

Subdwarf A subdwarf, sometimes denoted by "sd", is a star with luminosity class VI under the Yerkes spectral classification system. They are defined as stars with luminosity 1.5 to 2 magnitudes lower than that of main-sequence stars of the same ...

, a class of star * Surface detector, of cosmic rays at the

Pierre Auger Observatory The Pierre Auger Observatory is an international cosmic ray observatory in Argentina designed to detect ultra-high-energy cosmic rays: sub-atomic particles traveling nearly at the speed of light and each with energies beyond . In Earth's atmosphe ...

Electronics and computing

SD card Secure Digital (SD) is a proprietary, non-volatile, flash memory card format developed by the SD Association (SDA). Owing to their compact size, SD cards have been widely adopted in a variety of portable consumer electronics, including dig ...

(Secure Digital), a flash memory card format *

Software Distributor Software Distributor (SD) is the Hewlett-Packard company's name for their HP-UX software package management system. SD provides a set of tools for creating packages that will install software on a system running the HP-UX operating system. The pa ...

, an HP-UX system *

Standard-definition television Standard-definition television (SDTV; also standard definition or SD) is a television system that uses a resolution that is not considered to be either high or enhanced definition. ''Standard'' refers to offering a similar resolution to the ...

Super Density Disc The DVD (common abbreviation for digital video disc or digital versatile disc) is a digital optical disc data storage format. It was invented and developed in 1995 and first released on November 1, 1996, in Japan. The medium can store any kin ...

, an optical disc format *

Stable Diffusion Stable Diffusion is a deep learning, text-to-image model released in 2022 based on Diffusion model, diffusion techniques. The generative artificial intelligence technology is the premier product of Stability AI and is considered to be a part of ...

, a text-to-image generator

Mathematics

sd (elliptic function) In mathematics, the Jacobi elliptic functions are a set of basic elliptic functions. They are found in the description of the motion of a pendulum, as well as in the design of electronic elliptic filters. While trigonometric functions are define ...

, one of Jacobi's elliptic functions *

Standard deviation In statistics, the standard deviation is a measure of the amount of variation of the values of a variable about its Expected value, mean. A low standard Deviation (statistics), deviation indicates that the values tend to be close to the mean ( ...

(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 Service design is the activity of planning and arranging people, infrastructure, communication and material components of a service in order to improve its quality, and the interaction between the service provider and its users. Service design m ...

, holistic design of service experience *

Spiral Dynamics Spiral Dynamics is a model of developmental psychology Developmental psychology is the scientific study of how and why humans grow, change, and adapt across the course of their lives. Originally concerned with infants and children, the fiel ...

, a model of individual and societal development * '' Storm Data'', a US meteorological journal *

System dynamics System dynamics (SD) is an approach to understanding the nonlinear behaviour of complex systems over time using stocks, flows, internal feedback loops, table functions and time delays. Overview System dynamics is a methodology and mathematical ...

, of nonlinear systems

Other uses

* '' Sekolah Dasar'', term for primary school in Indonesia * Super D (cycling), a class of mountain bike race *

Super deformed ''Chibi'', also known as ''super deformation'' (''SD''), is an art style originating in Japan, and common in anime and manga where characters are drawn in an exaggerated way, typically small and chubby with stubby limbs, oversized heads, and ...

, an art style *

Sindhi language Sindhi ( ; or , ) is an Indo-Aryan language spoken by more than 30 million people in the Pakistani province of Sindh, where it has official status, as well as by 1.7 million people in India, where it is a Scheduled languages of India, schedu ...

(ISO 639-1 code: sd) * ''

sine die Adjournment ''sine die'' (from Latin 'without a date') is the conclusion of a meeting by a deliberative assembly, such as a legislature or organizational board, without setting a date to reconvene. The assembly can reconvene, either in its pres ...

'', Latin, undated (literally without a day)