Welcome to the definitions section of the Federal Aviation Regulations. This is one of the longer sections, thus will be broken into four parts. This is Acronyms and Rules of construction.
Acronyms and Rules of construction.

My explications are in small print after the definitions to which they apply.

AGL means above ground level.

ALS means approach light system. This is a rather cool system of lights. Lights shine either a specific color or specific pattern when an aircraft is on the correct approach path.

ASR means airport surveillance radar. These domes are seen around airports.

ATC means air traffic control.

CAS means calibrated airspeed. airspeed isn't how fast one is going. It is how fast the air is going over one's wings.

CAT II means Category II.

CONSOL or CONSOLAN means a kind of low or medium frequency long range navigational aid.

DH means decision height. Think: point of no return.

DME means distance measuring equipment compatible with TACAN. TACAN-Tactical Airborne Navigation DME is therefore a TACAN compatible component.

EAS means equivalent airspeed.

FAA means Federal Aviation Administration.

FM means fan marker.Those little squiggly paint marks on jet turbine intakes.

GS means glide slope.See soaring.

HIRL means high-intensity runway light system. These are NOT the blue lights, these are the bright white ones for night use at the ends of the runway.

IAS means indicated airspeed.

ICAO means International Civil Aviation Organization.

IFR means instrument flight rules.The most basic definition of IFR is flying when the weather is so bad that the instruments are the only thing one can fly with.

ILS means instrument landing system.

IM means ILS inner marker.

INT means intersection. of a runway

LFR means low-frequency radio range.

LOC means ILS localizer.

M means mach number.

MAA means maximum authorized IFR altitude.

MALS means medium intensity approach light system.

MALSR means medium intensity approach light system with runway alignment indicator lights.

MCA means minimum crossing altitude.

MDA means minimum descent altitude.

MEA means minimum en route IFR altitude.

MOCA means minimum obstruction clearance altitude.

MRA means minimum reception altitude.

MSL means mean sea level. this is the standard from which altitudes are usually given.

NDB(ADF) means nondirectional beacon (automatic direction finder).

OEI means one engine inoperative.

OM means ILS outer marker.

PAR means precision approach radar.

RAIL means runway alignment indicator light system.

RBN means radio beacon.

RCLM means runway centerline marking.

RCLS means runway centerline light system.

REIL means runway end identification lights.

RR" means low or medium frequency radio range station.

RVR means runway visual range as measured in the touchdown zone area.

SALS means short approach light system.

SSALS means simplified short approach light system.

SSALSR means simplified short approach light system with runway alignment indicator lights.

TACAN means ultra-high frequency tactical air navigational aid.

TAS means true airspeed.

TCAS means a traffic alert and collision avoidance system.

TDZL means touchdown zone lights.

TVOR means very high frequency terminal omnirange station.

VA means design maneuvering speed. This is the minimium speed the aircraft can go with its control surfaces still working.

VB means design speed for maximum gust intensity.

VC means design cruising speed.

VD means design diving speed.

VDF/MDF means demonstrated flight diving speed.

VEF means the speed at which the critical engine is assumed to fail during takeoff.

VF means design flap speed.

VFC/MFC means maximum speed for stability characteristics.

VFE means maximum flap extended speed.

VFTO means final takeoff speed.

VH means maximum speed in level flight with maximum continuous power.

VLE means maximum landing gear extended speed.

VLO means maximum landing gear operating speed.

VLOF means lift-off speed.

VMC means minimum control speed with the critical engine inoperative.

VMO/MMO means maximum operating limit speed.

VMU means minimum unstick speed.

VNE means never-exceed speed.

VNO means maximum structural cruising speed.

VR means rotation speed.

VREF means reference landing speed.

VS means the stalling speed or the minimum steady flight speed at which the airplane is controllable.

VS0 means the stalling speed or the minimum steady flight speed in the landing configuration.

VS1 means the stalling speed or the minimum steady flight speed obtained in a specific configuration.

VSR means reference stall speed.

VSRO means reference stall speed in the landing configuration.

VSR1 means reference stall speed in a specific configuration.

VSW means speed at which onset of natural or artificial stall warning occurs.

VTOSS means takeoff safety speed for Category A rotorcraft.

VX means speed for best angle of climb.

VY means speed for best rate of climb.

V1 means the maximum speed in the takeoff at which the pilot must take the first action (e.g., apply brakes, reduce thrust, deploy speed brakes) to stop the airplane within the accelerate-stop distance. V1 also means the minimum speed in the takeoff, following a failure of the critical engine at VEF, at which the pilot can continue the takeoff and achieve the required height above the takeoff surface within the takeoff distance.

V2 means takeoff safety speed.

V2min means minimum takeoff safety speed.

VFR means visual flight rules. Fly by looking out the window.

VHF means very high frequency.

VOR means very high frequency omnirange station.

VORTAC means collocated VOR and TACAN.

§  1.3  Rules of construction.

(a) In Subchapters A through K of this chapter, unless the context requires otherwise:

(1) Words importing the singular include the plural;

(2) Words importing the plural include the singular; and

(3) Words importing the masculine gender include the feminine.The FAA is NOT sexist...really...

(b) In Subchapters A through K of this chapter, the word:

(1) Shall is used in an imperative sense;

(2) May is used in a permissive sense to state authority or permission to do the act prescribed, and the words "no person may *    *    *" or "a person may not *    *    *" mean that no person is required, authorized, or permitted to do the act prescribed; and

(3) Includes means "includes but is not limited to".

G-P. Q-Z and acronyms

Federal Aviation Regulations