UDT
- Republic of Korea Navy
- Republic of Korea Navy UDT/SEAL
- U.S. Navy SEALs
- UDP-based Data Transfer Protocol
- Uitgeverij De Tijd
- Underdeck tonnage
- Underwater Demolition Team
- Union Démocratique Tchadienne
- Union démocratique du travail
- Union of Djibouti Workers
- United Dominions Trust
- União Democrática Timorense
- Urine diversion
- User-defined type