- South Dakota, a state of the United States of America.
- School district
- (law enforcement) Sheriff's department
- (medicine) Shacklesons Disease, a rare brain disease.
- (mathematics) Standard deviation, a mathematical measure of the spread of a list of numbers.
- (television) standard definition, SDTV
- Secure Digital, a non-volatile memory card format developed by Matsushita, SanDisk, and Toshiba for use in portable devices.