| sec | Migration Wizard Secondary IFF File |
| sec | PTC Creo Section Data |
| seco | MSX Configurator Software Update |
| secstore | Adobe Acrobat Security Store File |
| sedr | URAP Supplemental Experiment Data Record |
| see | LISCAD Database |
| seek | Word List Expert Seek List Data |
| seg | Mail.dat Segment File |
| seg2 | SEG-2 Data File |
| segd | SEG-D Data File |
| segy | SEG Y Data File |
| sel | LinkOne Selection List |
| sel | SAM hmmscore Selection Data |
| sem3d | SEMulator3D Model Data |
| seman | Xtext Semantics Data |
| semi | Spartan Semi-Empirical Data |
| sems | EcoStruxure Machine Expert SEMS Data |
| semul | WinZip Registration Data |
| senl | SAP Enable Now App Launcher |
| sense | LX-SenseAnnotator Sense Data |
| seo | SEO Note |
| seospider | Screaming Frog SEO Spider Data |
| sep | SEEP/W Data |
| sep | SimEnhancer Profile |
| sep | SWAT Septic Input Data |
| seq | CYANA Sequence File |
| seq | SAM sampleseqs Sequence Data |
| seq | Tinker Sequence |
| seq | Workswell Recorded Thermal Sequence |
| seq | XtalView Xfit Sequence Data |
