| Acronym | Meaning |
| CSC | Closed Spacelike Curve (relativity) - Computer Security Centre |
| IRN | Iran (ISO 3166 Trigram) |
| ACLU | American Civil Liberties Union |
| RU | Russia (ISO 3166 Digram) |
| ETT | Embedded Training Team |
| HM | Heard Island And McDonald Islands (ISO 3166 Digram; FIPS 10-4 Territory Code) |
| GCN | Gamma-ray Burst Coordination Network |
| DSS | Digitized Sky Survey - Discarding-Sabot Shell (ammunition) |
| TOT | Time On Target |
| REEF | Reef Environmental Education Foundation |