Hyperbole is a literary technique in which a certain piece of information, feeling, or other statement is exaggerated intentionally for a certain effect. In most cases, the literal interpretation of a hyperbole could not actually be true, but the exaggeration serves to emphasize a certain point. The statement "I have a million things that I have to do today," for example, is a hyperbole — it means that the speaker has many things to do, but it is unlikely that anyone actually needs to do a million tasks in one day. Hyperbole can also be used in literature sarcastically or for the sake of humor, though it is most commonly used for emphasis.
In prose, hyperbole is generally used for the purpose of emphasis or for humor. A writer who wants to make a particular point may make that point by overstating or exaggerating it. Hyperbole can be used in descriptions to emphasize some particularly prominent feature of a character, for instance. It can also be used to describe an action that is remarkable in some way. In these and other similar cases, hyperbole is used to place emphasis on a particular action, feeling, or feature and is not meant to be taken literally.
