Both hz and mhz are units of measure for frequency in addition to microprocessor speed.
Many people actually interact with hertz on a daily basis without realizing it by listening to music on their favorite radio stations.
Radio stations are broadcast using different radio wave frequencies. That's where the different station numbers on your radio dials come from.
Each number represents a different frequency, in this case, measured in megahertz.
Sound is also measured in Hz. Different frequencies are perceived by our ears to be different pitches.
Every single note on the keyboard has a different value in hertz, and in fact, every note has a range of frequencies, which is why instruments need to be tuned to sound right.
The speed at which computers can process information is measured in MHz.
Computers that perform high-difficulty tasks, such as processing 4K "ultra high resolution" graphics, require processing units with a higher value than simpler machines.
We interact with a wide variety of different frequencies every day, and most of them are measured in hertz or megahertz.