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.
V_A 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.
V_B Design speed for maximum gust intensity.
V_C Design cruising speed.
V_D Design diving speed.
V_DF Maximum demonstrated diving speed. Also M_DF, maximum demonstrated Mach No. in a dive.
V_E Maximum speed at which landing gear (or other item) may be extended or retracted (cycled).
V_FE Maximum flap extension speed (top of white arc on ASI).
V_H Maximum level-flight speed with maximum continuous power.
V_LE Maximum speed with landing gear extended.
V_MCA 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).
V_MU Minimum unstick speed.
V_NE Never-exceed speed.
V_MO Maximum operating speed. Also M_MO, maximum operating Mach No.
V_NO Normal operating speed. The maximum structural cruising speed allowable for normal operating conditions.
V_R Rotation speed, at which to raise the nose for take-off.
V_RA Rough-air speed. Maximum recommended airspeed for penetrating turbulent air.
V_REF Any reference or 'bug' speed, typically quoted for approach speeds.
V_S0 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 V_S, stalling speed 'clean', V_S1, stalling speed for a given configuration other than 'clean'.
V_SSE Minimum speed for deliberate shutting down of one engine for purposes of asymmetric flight training.
V_X Best angle of climb speed on all engines. Sometimes (UK usage) V_%.
V_XSE Best engine-out angle of climb speed.
V_Y Best rate of climb speed on all engines.
V_YSE Best engine-out rate of climb speed. Sometimes V_%SE.
V_ZRC Zero rate of climb speed (on one engine, where drag of inoperative engine reduces climb gradient to zero).