Hello!
The correct answer is "Hyperbole".
These are statements that are not meant to be taken literally, and very similar to idioms.
Example: She said she'd be there on time. Meh, took her about eight years.
This is a statement that is exaggerating the amount of time it took the subject to arrive. She didn't actually take eight years; she maybe was only a few minutes late.
Now, these are not to be confused with similes, which can be very similar depending on the way you use them.
Example of a similar simile (heh): He moves as fast as a cheetah when it comes to getting something he wants.
This can be confused with a hyperbole since it is also exaggerating the speed of the subject. However, a simile is meant to be used as a comparison, not just an exaggeration. This also applies to metaphors, as they are also comparisons, only lacking "like" or "as".
:)
