| Acronym | Meaning |
| SEMPA | Scanning Electron Microscopy With Polarization Analysis |
| SEMPI | Singly Excited Modified Perturbation Theory |
| SEN | Submerged Entry Nozzle |
| SENB | Single Edge Notched Beam |
| SEND | Surfaces Enhanced For Neat Desorption |
| SENSOR | Sentinel Event Notification Systems For Occupational Risks |
| SEP | Solar Energetic Particle (event) |
| SEP | Standard Error Of Prediction |
| SEP | Stimulated Emission Pumping |
| SEPA | State Environmental Policy Act |
| SEPAR | Surfaces Enhanced For Photolabile Attachment And Release |
| SEPP | State Environmental Protection Plan |
| SEPT | Secular Equation (with) Perturbation Theory |
| SERA | Sequential Electrochemical Reduction Analysis |
| SERC | State Emergency Response Commission |
| SERDP | Strategic Environmental Research And Development Program |
| SERDS | Shifted Excitation Raman Difference Spectroscopy |
| SEREX | Serological Identification Of Antigens By Recombinant Expre |
| SERHF | Symmetry-equivalenced Restricted Hartree-Fock |
| SERI | Solar Energy Research Institute |
| SERM | Selective Estrogen Receptor Modulator |
| SERODS | Surface-Enhanced Raman Optical Data Storage |
| SERON | Southern Regional Oxidant Network |
| SERRS | Surface-Enhanced Resonance Raman Spectroscopy |
| SERS | Surface Enhanced Raman Spectroscopy |
| SERT | Serotonin Transporter |
| SES | Surface Electronic State |
| SESAM | Semiconductor Saturable Absorber Mirror |
| SESAME | Second European Stratospheric Arctic And Midlatitude Experiment |
| SESAME | Simulation Of Electron Transport Supporting Analysis Of Materials |
| SESAO | Semiempirical Scaled Atomic Orbital |
| SESCA | Scanning Electron Spectroscopy For Chemical Applications |
| SESF | Superlattice Extrinsic Stacking Fault |
| SESFOD | Selective Excitation With Single Frequency Off Resonance Decoupling |
| SESMO | Semiempirical Scaled Molecular Orbital |
| SESR | Solvent Extraction And Soil Remediation |
| SET | Single Electron Transfer |
| SET | Single Electron Transistor |
| SET | Single Electron Tunneling |
| SETAC | Society Of Environmental Toxicology And Chemistry |
| SETB | Semiempirical Tight Binding |
| SETM | Statistical Electron Transfer Model (for Electron-exchange Collisions) |
| SETOC | International Sediment Exchange For Tests On Organic Contaminants |
| SETS | Superfund Enforcement Tracking System |
| SEU | Selective Excitation Unit |
| SEU | Single Event Upset (in Spacecraft Power Systems) |
| SEVB | Semiempirical Valence Bond |
| SEW | Site Electron-density Wave |
| SEXAFS | Surface-extended X-ray Absorption Fine Structure |
| SF CC | Space-fixed Close-coupled (equation |