Plain English Meaning
The elevator doesn't create energy — it just shifts it back and forth between speed and height. Pull back and you swap speed for altitude; push forward and you swap altitude for speed.
Full Definition
A term used to describe the elevator's role in trading the airplane's kinetic energy (airspeed) for potential energy (altitude), or vice versa, without adding or removing total energy from the airplane. Pitching up converts airspeed into altitude; pitching down converts altitude into airspeed. The throttle, by contrast, controls how much total energy the airplane has.
Context Anchor
Seen when learning how throttle and elevator together to , , airspeed, and altitude.