Megahertz measures frequency — how many times something repeats every second — and one megahertz is a million times per second. It is written MHz. You meet it in two places. Radio: an FM station sits at a place on the dial like 100.7 MHz, meaning its wave rises and falls a hundred million-odd times a second, and that number is simply the station's address. Computers: a chip's clock speed used to be given in megahertz (a 500 MHz processor ticks five hundred million times a second), though chips passed a thousand megahertz long ago and we now say gigahertz instead, so the megahertz mostly survives in radio, Wi-Fi, and older machines. Note the spelling: megahertz is the same in the singular and the plural — 'one megahertz', 'ninety megahertz', never 'megahertzes'. It is named after Heinrich Hertz, a German physicist who proved radio waves exist, which is why it keeps its capital H when abbreviated (MHz) even though the full word is lowercase. A faster clock speed is not automatically a faster computer, by the way — how much the chip does per tick matters just as much, and salespeople have quietly relied on customers not knowing that.

百萬赫、兆赫（收音機頻率、電腦時脈速度的單位，寫作 MHz，口語常直接講「兆赫」或英文 MHz）