Hyperbole is a term that refers to statements made in a particular work of fiction that are exaggerations of the actual truth of the matter. Often hyperboles are used as evidence in debates, and it can be very difficult to tell if a statement is hyperbole or not. A general rule is that if a claim is made that is completely out of league of anything ever shown in said universe (for example, if someone claimed to be a planetbuster in a verse where the strongest feats were citybuster), it's probably hyperbole. In universes with a wide range of characters on different tiers of power (such as Marvel and DC), this has to be evaluated on an individual character basis, instead of on the verse as a whole. For example, if someone in One Piece claimed they could destroy an island, it's reasonable to consider it a possibility, since other people in the verse have done comparable things (of course it still has to be evaluated based on the feats and powerscaling of the actual character). On the other hand, if someone said Spider-Man could destroy a star, it's not reasonable to think this is true despite the fact that Herald level characters and above in Marvel have done so, because Spider-Man is established as being on a lower tier than such characters.
Another way of determining hyperbole or not is to consider the likelihood that a character was misinformed, ignorant, lying, exaggerating, bluffing, mentally unstable, etc. when they made said statement. If there is not any evidence that they were, it can be taken more seriously. Of course, this method isn't as accurate as the feat scaling method above, and should only be relied upon if the first method doesn't give any clear answers.
Examples of hyperbole:
Cell saying he could destroy the solar system in Dragon Ball
Itachi's Amaterasu being as hot as the sun in Naruto
Yu Yu Hakusho characters claiming to be planetbusters
Samurai Deeper Kyo characters claiming to be FTL
Q from Star Trek being omnipotent
Reactron having the power to destroy a galaxy (Which only created a small crater)
Majin Buu and Dragon Ball GT characters claiming to be universe busters
The Sentry having the power of million exploding suns (this may actually have to be reevaluated based on some of his more recent feats)
Juggernaut being unstoppable (although against most opponents, he might as well be)
The black hole at the end of Diebuster creating a new Big Bang
Almost anything claimed in Touhou