Plain English Meaning
How fast the airplane is going down, measured in feet per minute. A 500 fpm descent rate means the airplane is losing 500 feet of altitude every minute.
Full Definition
The vertical speed at which an airplane is losing altitude, expressed in feet per minute (fpm) and shown on the vertical speed indicator (VSI). Descent rate is controlled primarily through pitch and power adjustments and is selected to suit the phase of flight, terrain, traffic, and passenger comfort.
Context Anchor
Seen during descents, approach planning, and any time a pilot is watching how quickly the airplane is moving downward.