A 'Hertz' is another word for 'cycles per second'. It is a measure of frequency and computer clock speed.
'Mega' is the metric term for one million.
So 1MHz is 1 million cycles per second
For example a computer running at 1MHz means that its internal clock is 'ticking' a million times per second. (By the way, that would be a *very* slow computer!)
Challenge see if you can find out one extra fact on this topic that we haven't already told you
Click on this link: MegaHertz