UCD
- UCD GAA
- Ultra compact dwarf
- Unicode Character Database
- Union of the Democratic Centre (Argentina)
- Union of the Democratic Centre (Spain)
- Union of the Democratic Centre (disambiguation)
- University College Dublin
- University College Dublin A.F.C.
- University College Dublin RFC
- University of California, Davis
- Unión Cívica Democrática
- Urine collection device
- Use case diagram
- User-centered design