V-speeds definitions

V1 Decision speed, up to which it should be possible to abort a take-off after failure of the critical engine and stop safely within the remaining runway length. After reaching V1 the take-off must be continued.
V2 Minimum take-off safety speed.
VA Design manoeuvring speed. The speed below which abrupt and extreme control movements are possible (though not advised) without exceeding the airframe's limiting load factors.
VB Design speed for maximum gust intensity.
VC Design cruising speed.
VD Design diving speed.
VDF Maximum demonstrated diving speed. Also MDF, maximum demonstrated Mach No. in a dive.
VE Maximum speed at which landing gear (or other item) may be extended or retracted (cycled).
VFE Maximum flap extension speed (top of white arc on ASI).
VH Maximum level-flight speed with maximum continuous power.
VLE Maximum speed with landing gear extended.
VMCA Minimum control speed (air). Minimum speed at which directional control of a multi-engined aircraft can be maintained after failure of critical engine (in effect, the lowest speed at which the aircraft possesses sufficient rudder authority to counteract the yaw induced by asymmetric thrust).
VMU Minimum unstick speed.
VNE Never-exceed speed.
VMO Maximum operating speed. Also MMO, maximum operating Mach No.
VNO Normal operating speed. The maximum structural cruising speed allowable for normal operating conditions.
VR Rotation speed, at which to raise the nose for take-off.
VRA Rough-air speed. Maximum recommended airspeed for penetrating turbulent air.
VREF Any reference or 'bug' speed, typically quoted for approach speeds.
VS0 Stalling speed at maximum take-off weight, in landing configuration with flaps and landing gear down, at sea level, ISA conditions (bottom of white arc on ASI). Also VS, stalling speed 'clean', VS1, stalling speed for a given configuration other than 'clean'.
VSSE Minimum speed for deliberate shutting down of one engine for purposes of asymmetric flight training.
VX Best angle of climb speed on all engines. Sometimes (UK usage) V%.
VXSE Best engine-out angle of climb speed.
VY Best rate of climb speed on all engines.
VYSE Best engine-out rate of climb speed. Sometimes V%SE.
VZRC Zero rate of climb speed (on one engine, where drag of inoperative engine reduces climb gradient to zero).