- 3C (Cross Cultural Competence)
- 3D (three-dimensional (geophysics))
- 3-D (Three-Dimensional)
- 3DA (Three-Dimensional Array)
- 3-DOF (Three Degree Of Freedom)
- 3DS (Digital Decision Display System)
- 3FDA (2,2-Bis (3,4-Dicarboxyphenyl) Hexafluoropropane Dianhydride)
- 3FG (Three-point field goal. Euroleague uses "3FG", while the NBA uses "3P"; North American media outlets, such as ESPN, generally (but not always) follow NBA practice.)
- 3G (Third Generation)
- 3GL (Third-Generation Programming Language)
- 3Gp (Third generation Partnership Project)
- 3GPP (mobile broadband "3G" Partnership Project)
- 3IBILA (3rd Independent Battery Iowa Light Artillery - Dubuque Battery)
- 3JR (Third Battalion Jamaica Regiment)
- 3M (Maintenance and Material Management (3M System))
- 3MC (Maintenance Material Management Coordinator)
- 3MVI (3rd Regiment Infantry Maryland Volunteers)
- 3NF (Third Normal Form)
- 3NT (Bridge bid to take 9 tricks, No Trump)
- 3P (proved, probable and possible reserves)
- 3R3 (3.3 ohm Resistor)
- 3RS (Reading, wRiting and aRithmetic)
- 3SR (Three Station Rotating)
- 3USVI-I (Galvanized Yankees Company I, 3rd United States Volunteer Infantry)
- 3VA (The council for voluntary service for Eastbourne, Lewes District and Wealden)
- 3VAVI (3rd Regiment Virginia Volunteer Infantry)
- 3WW (threewordwednesday)
- 3XMAG (3X Magnifier lens)