| Meaning | Category |
| 2D or 3D CAD model Initial Graphics Exchange Specification format | Computing->File Extensions |
| Image Systems Grayscale | Computing->File Extensions |
| Inner Gulf Shelf | Academic & Science->Ocean Science |
| Insoluble Glue Substances | Academic & Science->Chemistry |
| Institute of Geological Sciences | Academic & Science->Geology |
| Instrument Guidance System | Governmental->Transportation |
| Instrument Guiding System | Governmental->Military |
| Interchange Group Separator | Computing->General |
| Intermediate General Support | Governmental->Military |
| International Games System | Community->Sports |
| International Glaciological Society | Academic & Science->Ocean Science |
| International Gps Service | Governmental->US Government |
| Internet Go Server | Internet |
| Ipswich Grammar School | Community->Educational |
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