SD or sd is an acronym that may mean:

• Sales and Distribution, business
• San Diego, a U.S. city
• SanDisk, US-based multinational corporation which designs and markets flash memory card products
• SafeDisc, a CD/DVD copy protection solution by Macrovision Corporation
• Secure Digital, flash memory card format used in portable device, including digital cameras and handheld computers
• Sicherheitsdienst, Security Police, the intelligence service of the Nazi SS
• Snare drum
• Social Democrats (Slovenia), a left-wing Slovenian political party
• Software Distributor, an HP-UX software package management system
• South Dakota, a U.S. state
• Standard-definition television
• Standard Deviation, statistics
• Stronnictwo Demokratyczne, a defunct Polish party
• Sudan, ISO country code
• Sudan Airways, IATA airline designator
• Super Deformed, an exaggerated drawing style used in anime and manga
• Super Dollfie, a doll by Japanese company Volks
• Suppressed, a suffix placed at the end of a firearm's model name to note it is fitted with a suppressor.
• Sustainable Development, a system of developing, mainly agriculture in the Third World
• Significant digits, a method of expressing error in measurement
• SharpDevelop, a free and open source IDE for the C# Visual Basic .NET programming languages
• Sueloise Dominion or Sueloise Dating

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