A simile is a figure of speech that directly compares two things that are unlike. Similes use the words "as" or "like" to draw comparisons.
Similes help readers to better understand what an author is trying to convey within a text. For instance, the simile "swims like a fish" helps to illustrate that the subject is a good swimmer. In the simile "runs like a cheetah," a reader can gather that the subject runs fast.
Similes differ from metaphors, which also help to draw comparisons. Unlike similes, metaphors are indirect comparisons and do not involve the use of the words "like" or "as."