Plain English Meaning
How fast the airplane is going down, measured in feet per minute.
Full Definition
The rate at which an aircraft is descending, measured in feet per minute (fpm). Shown on the vertical speed indicator (VSI) as a downward reading.
Context Anchor
You will see this term in descent, approach, and landing discussions, especially when judging whether the airplane is coming down too fast or too slowly.
Derivation
"Sink" comes from the Old English sincan, meaning to fall or settle downward. In aviation it kept its everyday sense — the airplane is settling toward the ground — but added a measurable rate to it.
Why Pilots Care
Managing sink rate prevents hard landings and maintains safe energy management near the ground.