| syn | COREX Syntactic Annotations |
| syn | Microsoft Word Synonym Data |
| syn | TextPad Syntax File |
| sync | Apple ColorSync Data |
| syncconflict | iTunes Synchronization Conflict Data |
| syncdb | iTunes Sync Database |
| synciddb | SQLite Data |
| syncml | Open Mobile Alliance SyncML Data |
| synctex | SyncTeX Data |
| syo | SYSTAT Output Data |
| syr | Xilinx XST Synthesis Report |
| sys | General Swap File |
| sys | Microsoft SQL Server Data Replication System Table Data |
| sysex | MIDI System Exclusive Message |
| syx | MIDI System Exclusive Message |
| syz | SYSTAT Data |
| sy_ | Compressed SYS File |
| sz | Smokeview Sizing Information Data |
| sz | WinAMP Skin |
| sz3 | Scream Tracker 3 Data |
| sz4 | E-triloquist Phrase Library |
| szl | Tecplot 360 CFD Results Data |
| szplt | Tecplot 360 CFD Results Data |
| szs | Wii Game Data |
| szt | Super ZZT Game Creation System Data |
| szx | Spectaculator ZX-State Snapshot |
| szz | Smokeview Sizing Information Data |
| t | Corel Paradox Database |
| t$ab | Timbuktu Pro Address Book Data |
| t$m | AVG Internet Security Temporary File |
