| syl | Symbolic Link Spreadsheet |
| sylk | Symbolic Link Spreadsheet |
| sym | gEDA Symbol Data |
| sym | PTC Creo Drawing Symbol Data |
| sym | VariCAD Symbol Library |
| sym | Vector CAD Variables Data |
| symbols | Debian Package Extended Shared Library Information Data |
| symcache | Microsoft Windows Symbol Cache |
| syn | Adobe RoboHelp Synonym List |
| syn | Concordance Synonyms Data |
| syn | COREX Syntactic Annotation Data |
| 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 |
