Definition
A unit of frequency equal to one complete repetition of a wave or oscillation occurring in one second. Now formally replaced by the hertz (Hz), where one cycle per second equals one hertz.
Plain English
How many full back-and-forth movements something makes in one second. If a wave repeats sixty times each second, that is sixty cycles per second.
Context Anchor
Seen in aircraft electrical-system, radio-signal, and vibration discussions, especially in older references that use “cycles per second” instead of “hertz.”
Derivation
Cycle comes from the Greek kyklos, meaning a circle or wheel — something that returns to where it started. A cycle per second is simply one complete return repeated each second. The term was replaced by hertz in honor of physicist Heinrich Hertz, who demonstrated radio waves.
Why Pilots Care
Aircraft electrical and radio systems are rated in frequency. Reading older manuals or placards, a pilot may see cycles per second instead of hertz and needs to recognize they mean the same thing.
Analogy
A clock that ticks once each second is making one tick per second. A repeating wave at one cycle per second completes one full repeat in that same amount of time.
Intuition Check
Do not read “cycle” here as an engine operating cycle or a training cycle. Here it means one complete repeat of a wave or vibration.
Example Sentence 1
The older radio placard listed the frequency in cycles per second rather than hertz.
Example Sentence 2
Some navigation signals use audio tones measured in cycles per second to identify the station.