Definition
A periodic pulsing variation in sound or signal amplitude produced when two waves of slightly different frequencies combine. The beat frequency is equal to the difference between the two source frequencies.
Plain English
When two tones or signals are very close in frequency but not identical, they blend in a way that produces a slow, repeating throb. That throb is the beat, and how fast it pulses tells you how far apart the two frequencies are.
Context Anchor
Commonly noticed in multiengine propeller airplanes when the engines or propellers are not turning at exactly the same speed.
Derivation
From Old English 'beatan,' to strike repeatedly. The pulsing rise and fall in volume sounds like a steady striking, which is where the name comes from.
Why Pilots Care
Unsynchronized engines create annoying beats that increase fatigue and can mask other sounds important for situational awareness.
Analogy
It is like hearing two fans running at almost the same speed. Instead of one steady sound, you hear the sound swell and fade in a slow pulse.
Intuition Check
Beat does not mean to hit or defeat something here. It means a repeating pulse in sound or vibration caused by two nearly matching sources.
Example Sentence 1
The pilot adjusted the right engine RPM until the beat in the cabin faded, indicating the propellers were synchronized.
Example Sentence 2
A faint beat in the headset indicated the VOR signal was being received from two stations at once.