| tra | WinTrack Railroad Track |
| trace | VMware ThinApp Binary Trace Log |
| trak | NI Traktor Pak File |
| trans | Amaya Transformations Data |
| trashinfo | Linux Trash Storage Metadata |
| traw | PLINK Variant-major Additive Component File |
| tray | CorelDRAW Corel CONNECT Tray Data |
| trb | HP Printer Diagnostic Package |
| trbw | STAR-CCM+ TurboWizard File |
| trc | Lattice Reveal Analyzer Waveform Data |
| trd | TrID Definitions Package |
| tree | Es-Builder v3 Tree File |
| treedb | TreeDBNotes Options Data |
| treefile | GDE Phylogenetic Tree Data |
| trf | BrainVoyager QX Transformations Data |
| trf | LFToolkit Transformation Rules File |
| trg | SQL Script Triggers |
| tri | FreeSurfer Triangular Surface Data |
| tri | Greg Hood Binary Triangles Data |
| tri | Neuroscan Triangulated Surface Data |
| tri | Ribbons Triangle Definition |
| tria | Greg Hood ASCII Triangles Data |
| trib | Greg Hood Binary Triangles Data |
| trie | Trie Data |
| triggers | Debian Package Triggers Data |
| triple-s | Triple-S Survey Data |
| trj | GROMACS Trajectory of a Simulation Data |
| trk | Garmin GPS PCX5 Tracklog |
| trk | MakeMusic Finale Track/Staff Mapping File |
| trk | STAR-CD v4 Droplet Track Data |
| trl | Holux GM-101 Tracklog |
| trl | Topocad Roadlines |
| trn | CFX Transient File |
| trn | Microsoft SQL Server Transaction Log |
| trn | Oracle Documaker Transaction Data |