Definition
The rate at which an object moves through space, expressed as distance covered per unit of time. In aviation, speed is most often stated in knots (nautical miles per hour) and may be measured relative to the air mass (airspeed) or relative to the ground (groundspeed), depending on context.
Plain English
How fast something is moving, usually measured in knots in aviation.
Context Anchor
Seen on the airspeed indicator, in performance charts, on checklists, and in pilot discussions about takeoff, climb, cruise, approach, and landing.
Derivation
From the Old English 'sped,' meaning success, prosperity, or swiftness. Over time, the meaning narrowed to refer specifically to swiftness or rate of motion.
Why Pilots Care
Speed is one of the most fundamental quantities a pilot manages. Every phase of flight has target speeds — for takeoff, climb, cruise, approach, and landing — and flying outside those speeds can compromise control, performance, or structural safety.
Intuition Check
Do not assume speed always means the number on the airspeed indicator. In aviation, speed must be understood with its reference: through the air, over the ground, or another stated measurement.
Example Sentence 1
The pilot reduced speed before extending the flaps for landing.
Example Sentence 2
Reducing speed too quickly in the traffic pattern can lead to a stall.