What is the term for an exaggeration used for emphasis or effect?

The correct term for an exaggeration used for emphasis or effect is hyperbole. Hyperbole is a common literary device that involves making statements that are obviously exaggerated to create a strong impression or to convey feelings in a dramatic way. For instance, when someone says, "I've told you a million times," they are not literally counting repetitions but emphasizing their frustration or the frequency of their communication.

In contrast, other terms provided do not capture this specific meaning. A simile involves a comparison between two different things using "like" or "as," but it does not inherently involve exaggeration. An understatement refers to minimizing something for effect, making it the opposite of hyperbole. A metaphor is a direct comparison stating that one thing is another, which also does not imply exaggeration. Hence, hyperbole stands out as the term that accurately describes the use of exaggeration for emphasis.