-- V1ROT8 -- seen on some fast car some years ago
V1 is a v-speed, in aircraft terminology v-speeds are specific speeds for various operations. Takeoff speed is V2, maximum speed with landing gear extended is VLE, maximum speed with flaps extended is VFE. These speeds vary from model to model & so its important for pilots to familiarize themselves with the v-speeds of any aircraft they intend to fly.
V1 is the maximum speed during takeoff at which a pilot can safely stop the aircraft without leaving the runway. This is also the minimum speed that allows the pilot to safely continue (to V2 takeoff) even if a critical engine failure occurs (between V1 and V2).
So basically V1 is the point of no return, once youve hit V1, you are committed to the takeoff, even if you lose an engine you're better off flying than you are trying to stop.
from answers.com
