SAD

The word sad refers to an emotional condition; see sadness or the for more.

The acronym SAD may refer to:
* Sagittal Abdominal Diameter, the diameter around one's waistline
* Schizoaffective disorder, a psychiatric diagnosis with symptoms of a mood disorder and schizophrenia
* Seasonal affective disorder, a mood disorder with depressive symptoms in the winter
* Separation anxiety disorder, a psychological condition related to anxiety of separation from home or from people
* Sexual arousal disorder, the inability to attain or maintain typical responses to sexual arousal
* Selected area diffraction, a crystallographic experimental technique that can be performed inside a transmission electron microscope
* Shiromani Akali Dal, an Indian political party
* Silicon Avalanche Diode, an electronic component
* Singles Awareness Day, a humorous holiday celebrated on February 14
* Small angle diffraction, a technique for analysing materials
* Social anxiety disorder, a diagnosis referring to excessive anxiety in social situations
* Software architecture document, a document for the architecture of computer software
* Special Activities Division, the Central Intelligence Agency's special operations force in the United States
* Standard American Diet, a phrase associated with diet-related obesity in the United States
* Sum of absolute differences, a simple metric for motion estimation in video compression
* Systems Analysis and Design, an interdisciplinary part of science

Sad can also mean:
* Ṣād, a letter of the Arabic alphabet ( _ar. ﺹ).
* Sad (sura), the 38th sura of the Qur'an (named after the letter)
* Sad, Podlaskie Voivodeship (north-east Poland)
* Sad, Dnipropetrovsk Oblast, an urban-type settlement in Dnipropetrovsk Oblast, Ukraine