Plain English Meaning
A way of training that takes the pilot beyond ordinary straight-and-level flying so they learn to fly the airplane through steep banks, high and low pitch attitudes, and the slow and fast ends of its speed range. The goal is to be comfortable and capable across the whole range of what the airplane can do.
Full Definition
A method of flight instruction that deliberately exposes the pilot to the airplane's full range of attitudes (pitch and bank angles) and its full performance envelope (speeds, load factors, and angles of attack), rather than limiting practice to the narrow band of normal cruise, climb, and . The intent is to build and for , , and upsets so the pilot can handle the airplane confidently anywhere within its limits.