| Acronym | Meaning |
| IAUC | International Astronomical Union Circular |
| HO | Holmium |
| FYI | For Your Information |
| SBB | German For The Swiss Federal Railways |
| MSEC | Message Security Encryption Code (emm-sec) |
| AR | Argentina (FIPS 10-4 Country Code; ISO 3166 Digram) - Arkansas (postal Symbol) - Armour |
| USN | United States Navy |
| Q4 | Fourth Quarter |
| MEX | Mexico (ISO 3166 Trigram) |
| SPST | Single-Pole Single-Throw |