Plain English Meaning
Flying by setting the airplane's nose position and wing angle to a known picture, then adjusting power to match — instead of chasing individual instruments. Pick the right attitude and power, and the airplane does what you want.
Full Definition
A method of controlling an airplane by establishing and maintaining specific pitch and bank attitudes in relation to the natural horizon (or the attitude indicator), combined with appropriate power settings, to produce a desired performance such as a climb, descent, level flight, or turn.