| Acronym | Meaning |
| RRN | Recurrence Rate Number |
| STP | S?o Tom? And PrĀncipe (ISO 3166 Trigram) -Standard Temperature And Pressure |
| GYY | Gary/Chicago International Airport (IATA Airport Code) |
| IK | Inupiaq Language (ISO 639-1 Code) |
| NNO | Norwegian Nynorsk Language (ISO 639-2 Code) |
| IY | Iraqi-Saudi Neutral Zone (FIPS 10-4 Territory Code; Obsolete 1993) |
| BRDM | Boyevaya Razvedyvatelnaya Dosornaya Mashina (Russian ?????? ???????????????? ???????? ?????? |
| PF | French Polynesia (ISO 3166 Digram) - Petafarad -Phenol Formaldehyde (resin) |
| TDM | Time-Division Multiplexing |
| HAZ | Heat-Affected Zone |