Critical engine failure recognition speed
V1 is the minimum speed in the takeoff, following a failure of the critical engine at VEF, at which the pilot can continue the takeoff with only the remaining engines. Any problems after V1 are treated as inflight emergencies.
In the case of a balanced field takeoff, V1 is 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 and the minimum speed at which the takeoff can be continued and achieve the required height above the takeoff surface within the takeoff distance. In this context, V1 is the takeoff decision speed.

Other presentation: V1 is the maximum speed where an action must occur to stop the airplane on the runway and the minimum speed at which the takeoff can be continued following the recognition of an engine failure and achieve the required height above the takeoff surface.

Other presentation from Boeing: It was determined in 1992 that the existing definition of V1 might have caused confusion because they did not make it clear that V1 is the maximum speed at which the flight crew must take the first action to reject a takeoff. As a result, the FAA has changed the definition of V1 in FAR Part 1 to read as follows:

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

Minimum Control Speed (GROUND)
The speed which correspond to an engine failure at VMCG plus the speed gained during one second following the engine failure.
It is the V1 minimum speed.

Take Off safety speed
Also called takeoff screen speed, the minimum speed in the second segment of a climb following an engine failure.
V2 is the normal engine inoperative initial climb speed.
Minimum V2 must be equal to or greater than 1.13 VS1g and 1.1 VMCA

Steady climb speed with all engines operating to be achieved by 400 ft gross height

Design maneuvering speed
It is a stalling speed at the maximum legal G-force and hence the maximum speed at which abrupt, full deflection, control inputs will not cause the aircraft to exceed its G-force limit).
Maneuvering speed is limited by aircraft structural characteristics.

Best endurance speed
The speed that gives the greatest airborne time for fuel consumed. This may be used when there is reason to remain aloft for an extended period, such as waiting for a forecast improvement in weather on the ground.

Best power-off glide speed
The speed that provides maximum lift-to-drag ratio and thus the greatest gliding distance available.

Design diving speed
Usually 1.4 × VNO.

Velocity Engine Failure
The Calibrated Airspeed at which the critical engine is assumed to fail during takeoff.

Maximum flap extended speed
Different maximum speeds may be specified for partial flap extension.
Top of white arc on many airspeed indicators.

Maximum landing gear extended speed
The maximum speed at which the aircraft may be flown with the landing gear extended
VLE is always higher than VLO

Maximum landing gear operating speed
The maximum speed at which the aircraft may be flying while raising or lowering the gear.
VLO is always lower than VLE

Maximum Brake Energy speed
The maximum speed at which the wheel brakes have demonstrated the ability to absorb the energy required to stop the airplane for the takeoff conditions.

Never-exceed speed
Red line and top of yellow arc on many airspeed indicators.

Rotation speed
The speed of an aircraft at which the pilot initiates rotation to obtain the scheduled takeoff performance. It must be greater or equal to the V1 speed.
VR >= 1.05 VMCA

Stall speed
The stalling speed or the minimum steady flight speed at which the airplane is controllable. Usually synonymous with VS1, stall speed in a specified configuration.
Bottom of green arc on many airspeed indicators.

The stalling speed or the minimum steady flight speed in the landing configuration.
Bottom of white arc on many airspeed indicator.

The stalling speed or the minimum steady flight speed obtained in a specific configuration (usually a configuration "clean" of flaps, landing gear and other sources of drag).

Speed for best angle of climb
This provides the best altitude gain per unit of horizontal distance, and is usually used for clearing obstacles during takeoff.

Speed for best rate of climb
This provides the best altitude gain per unit of time.