Plain English Meaning
How fast the airplane is going down, measured in how many feet of altitude it loses each minute.
Full Definition
The vertical speed at which an aircraft is losing altitude, expressed in feet per minute (fpm) and indicated by the vertical speed indicator (VSI).
Context Anchor
Seen when discussing glides, gliding turns, landing approaches, and any situation where the pilot must judge how quickly the airplane is losing height.
Derivation
Rate comes from an older meaning of a measured amount, and descent comes from Latin words meaning “to climb down.” Together, the phrase points to a measured amount of downward movement over time.