Plain English Meaning
It is a way of measuring how fast a radio signal vibrates. One MHz means the signal completes one million back-and-forth cycles every second.
Full Definition
A unit of frequency equal to one million cycles per second. In aviation it is most often used to describe radio frequencies for voice communication and navigation.
Context Anchor
Seen when tuning aircraft radios, reading maintenance information for antennas and aircraft electronics, or checking the frequency range of installed equipment.
Derivation
From 'mega' (Greek for 'great' or 'large', used in science to mean one million) and 'hertz', named after Heinrich Hertz, a German physicist who proved radio waves exist. So megahertz literally means 'a million hertz' — a million cycles per second.