Plain English Meaning
Make your power change a little early, just before the airspeed reaches the number you want. The airplane takes a moment to settle, so if you wait until you see the target speed, you'll overshoot it.
Full Definition
A power-and-pitch control technique in which the pilot adjusts the throttle (and pitch as needed) before the airspeed indicator reaches the desired value, so that by the time the aircraft stabilizes, the airspeed settles exactly on target. Because the airplane and engine respond gradually, control inputs must be made in anticipation of the desired airspeed rather than in reaction to it.
Context Anchor
Used in when changing power or pitch to and a target airspeed.