| Acronym | Definition |
|---|
| ISSU | In Service Software Upgrade (system software upgrade without service interruption) |
| ISSU | in Service Software Upgrades |
| ISSU | Independent State Store Union (Pennsylvania) |
| ISSU | International Student Support Unit (Australia) |
| ISSU | Indigenous Schooling Support Unit (Australia) |
| ISSU | Islamic Society of Stanford University |
| ISSU | Idaho Steelhead and Salmon Unlimited (Idaho) |
| ISSU | India Sunday School Union (est. 1876) |
| ISSU | Integrated Support Services Unit (California) |
| ISSU | Interface Signal Switching Unit (SQQ-28) |
| ISSU | Irish Secondary Schools Union (Ireland) |