Def
- DEF II
- Danish EL-Federation
- Deaf (disambiguation)
- Def (instrument)
- Def American
- Def Jam Recordings
- Def Jef
- Def Jux
- Def Leppard
- Defcon (disambiguation)
- Delphi Economic Forum
- Design Exchange Format
- Diesel exhaust fluid
- Diethylformamide
- Disarmed Enemy Forces
- Drawing Exchange Format
- Mos Def
- Oskar Schindler's Enamel Factory
- PostScript
- Python syntax and semantics
- So So Def Recordings