V 1

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. V 1 also means the minimum speed in the takeoff, following a failure of the critical engine at V EF , at which the pilot can continue the takeoff and achieve the required height above the takeoff surface within the takeoff distance.

Source: 14 CFR § 1.2