Occasionally you may see an abbreviation or two on this or other aviation related sites.
If you're not a pilot, you may find the following helpful.
| AGL | above ground level |
| ALS | approach light system |
| ASR | airport surveillance radar |
| ATC | air traffic control |
| CAS | calibrated airspeed |
| CAT II | Category II |
| CONSOL | a kind of low or medium frequency long range navigation aid |
| DH | decision height |
| DME | distance mesuring equipment compatable with TACAN |
| EAS | equivalent airspeed |
| FAA | Federal Aviation Administration |
| FM | fan marker |
| GS | glide slope |
| HIRL | high intensity runway light system |
| ICAO | International Civil Aviation Organization |
| IFR | instrument flight rules |
| ILS | instrument landing system |
| IM | ILS inner marker |
| INT | intersection |
| LDA | localizer-type directional aid |
| LFR | low-frequency radio range |
| LMM | compass locator at middle marker |
| LOC | ILS localizer |
| LOM | compass locator at outer marker |
| M | mach number |
| MAA | maximum authorized IFR altitude |
| MALS | medium intensity approach light system |
| MALSR | medium intensity approach light system with runway alignment indicator lights |
| MCA | minimum crossing altitude |
| MDA | minimum decent altitude |
| MEA | minimum enroute IFR altitude |
| MM | middle marker |
| MOCO | minimum obstruction clearance altitude |
| MSL | mean sea level |
| NDB (ADF) | nondirectional beacon (automatic direction finder) |
| NOPT | no proceedure turn required |
| OEI | one engine inoperative |
| OM | ILS outer marker |
| PAR | precision approach radar |
| RAIL | runway alignment indicator light system |
| RBN | radio beacon |
| RCLM | runway centerline marking |
| REIL | runway end identification lights |
| RR | low or medium frequency radio range station |
| RVR | runway visibility range as measured in the touchdown zone area |
| SALS | short approach light system |
| SSALS | simplified short approach light system |
| SSALSR | simplified short approach light system with runway alignment indicator lights |
| TACAN | ultra-high frequency tactical air navigation aid |
| TAS | true airspeed |
| TCAS | traffic alert and collision avoidance system |
| TDZL | touchdown zone lights |
| TVOR | very high frequency terminal omnirange station |
| VA | design maneuvering speed |
| VB | design speed for maximum gust intensity |
| VC | design cruising speed |
| VD | design diving speed |
| VDF/MDF | demonstrated flight diving speed |
| VF | design flap speed |
| VFC/MFC | maximum speed for stability characteristics |
| VFE | maximum flap extended speed |
| VH | maximum speed in level flight with maximum continous power |
| VLE | maximum landing gear extended speed |
| VLO | maximum landing gear operating speed |
| VLOF | lift-off speed |
| VMC | minimum control speed with critical engine inoperative |
| VMO/MMO | maximum operating limit speed |
| VMU | minimum unstick speed |
| VNE | never-exceed speed |
| VNO | maximum structural cruising speed |
| VR | rotation speed |
| VS | stall speed or the minimum steady flight speed at which the airplane is controllable |
| VS0 | stall speed or the minimum steady flight speed in the landing configuration |
| VS1 | stall speed or the minimum steady flight speed obtained in a specified configuration |
| VTOSS | takeoff safety speed for Category A rotorcraft |
| VX | speed for best angle of climb |
| VY | speed for best rate of climb |
| V1 | takeoff decision speed |
| V2 | takeoff safety speed |
| V2 min | minimum takeoff safety speed |
| VFR | visual flight rules |
| VHF | very high frequency |
| VOR | very high frequency omnirange station |
| VORTAC | collocated VOR and TACAN |