| FUD | Fear Uncertainty Doubt | Computer and Internet |
| FUTAB | Feet Up, Take A Break | Message › Chat |
| FUSE | Far Ultraviolet Spectroscopic Explorer | Science and Technology › Physics |
| FU | Freak You | Message › Chat |
| FUBB | Fouled Up Beyond Belief | Message › Chat |
| Fum | Fumbles | Arts and Sports › Football |
| FUBAR | Fouled Up Beyond All Recognition | Message › Chat |
| FUD | Face Up Deal | Message › Chat |
| FTP | File Transfer Protocol | Computer and Internet › Networking |
| Fr | Francium | Chemistry |