Subsonic may refer to:
- Any speed lower than the speed of sound within a sound propagating medium is called subsonic
- Subsonic aircraft, a flying machine that flies at air speeds lower than the speed of sound
- subsonic flight, an aircraft flight at air speeds lower than the speed of sound in air
- Subsonic and transonic wind tunnel
In computing:
- SubSonic (software), an open source object-relational mapper for .NET
- Subsonic (media server), an open source media server
See also:
- Infrasound, sound at frequencies below the normal threshold of human hearing