1. (uncountable) Extreme exaggeration or overstatement; especially as a literary or rhetorical device.
2. (uncountable) Deliberate exaggeration.
3. (countable) An instance or example of this technique.
4. (countable, obsolete) A hyperbola.

Usage notes

• When used as a literary device, hyperbole is an exaggeration that, while not intended to be taken literally, still describes a situation or image that is at least feasible or possible. Exaggeration that is considered impossible is called adynaton.

  Examples: “I have been waiting for hours for the end of your ‘short’ coffee break.” is a hyperbole while “I have been waiting for ages for the end of your ‘short’ coffee break.” is an adynaton.

• This distinction is not always observed, even in textbooks.

See wiktionary for more, or consider wikipedia as well, which says, amongst other things:

It may be used to evoke strong feelings or to create a strong impression, but is not meant to be taken literally. [...] Hyperbole is used to create emphasis. It is a literary device often used in poetry, and is frequently encountered in casual speech.

I use hyperbole when I write, and often it gives me headaches. “Will this post be read by and responded to by some pedantic literalist that can’t stand any figures of speech? Maybe. Should I include a disclaimer pointing out it is an intentional exaggeration?”

No, I don’t want to. It’s a pain and disclaimers ruin posts. My goal is to use hyperbole correctly, sparingly, usefully. If I too liberally sprinkle hyperbole, call me on it, and I’ll reduce it. I should be using it only when it is reasonable to expect native English speakers to understand it correctly.

And the goal with this particular post is to have something to point people at (thus a disclaimer that applies to all future posts), and possibly a place to discuss hyperbole in general, when it’s useful, when it isn’t, etc.