| Meaning | Category |
| IRIS Spinning Stage | Governmental->NASA |
| Immigrant Social Services | Governmental->US Government |
| Impotent Sea Snakes | Miscellaneous->Funnies |
| Imprinted Sportswear Show | Community->Conferences |
| In School Suspension | Community->Educational |
| In-School Suspension | Community->Schools |
| Inclination Sensor System | Academic & Science->Ocean Science |
| Indiana Science Standards | Community->Educational |
| Inertial Subsystem | Governmental->NASA |
| Information Systems Security | Governmental->Military |
| Inhibit/Override Summary Snapshot Display | Governmental->NASA |
| Initial Send Sequence | Computing->Networking |
| Injury Severity Score | Medical->Physiology |
| Input to State Stability | Academic & Science->Physics |
| Inspection Selection System | Governmental->Military |
| Installation Support Services | Governmental->NASA |
| Instant Space Station | Miscellaneous->Funnies |
| Institute Of Silly Strings | Miscellaneous->Funnies |
| Institute of Social Studies | Academic & Science->Universities |
| Instruction Summary Sheet | Governmental->NASA |
| Instructional Support Staff | Academic & Science->Universities |
| Instrument Sales And Service | Business->General |
| Integrated Sounding System | Academic & Science->Ocean Science |
| Integrated Support Stand | Governmental->NASA |
| Integrated System Schematic | Governmental->NASA |
| Integrated Systems Support | Governmental->Military |
| Intelligence Systems Secretariat | Governmental->US Government |
| Interactive Survivability Simulation | Governmental->Military |
| International Space Station | Governmental->NASA |
| International Students Service | Academic & Science->Universities |
| International Superstar Soccer | Community->Sports |
| International Switching Symposium & ICS | Academic & Science->IEEE |
| Internet Security Service | Internet |
| Internet Server Supplement | Computing->Networking |
| Ion Scattering Spectrometry/Spectroscopy | Academic & Science->Electronics |
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