Plain English Meaning

The narrow speed window at high altitude where the aircraft is flying fast enough not to stall but slow enough not to hit shock-wave shaking. Fly too slow, the wing buffets from low speed; fly too fast, it buffets from going too close to the speed of sound.

Full Definition

The upper and lower airspeed limits, at a given weight and altitude, between which an aircraft can fly without encountering buffet. The lower limit is the low-speed (stall) buffet, where the wing is approaching its critical angle of attack. The upper limit is the high-speed (Mach) buffet, where airflow over the wing reaches a Mach number high enough to form shock waves and disturb the airflow. As altitude increases, these two limits .