Plain English Meaning
How quickly the airplane is changing the direction it is pointing, measured in degrees per second.
Full Definition
The rate at which an aircraft changes its heading during a turn, expressed in degrees per second. A standard rate turn is 3 degrees per second, which produces a complete 360-degree turn in two minutes. Rate of turn depends on bank angle and true airspeed: for a given bank angle, increasing airspeed decreases the rate of turn; for a given airspeed, increasing bank angle increases the rate of turn.
Context Anchor
Seen when learning turn radius, bank angle, airspeed, instrument turns, and how much room an airplane needs to complete a turn.
Derivation
Rate comes from an old word meaning a measured amount. Here it means a measured amount of time. Turn keeps its meaning: changing direction. Together, rate of turn means how much the airplane’s direction changes in a given amount of time.