What is a comparison between two things using the words 'like' or 'as' called?

The term you are looking for is a simile, which is a figure of speech that directly compares two different things using the words "like" or "as." This literary device is effective in creating vivid imagery by emphasizing similarities between the two entities. For example, saying "as brave as a lion" draws a connection that helps the reader understand the level of bravery being described through a familiar image.

In contrast, a metaphor is a different type of comparison that implies a direct equivalence between two things without using "like" or "as." An oxymoron combines contradictory terms to create a new meaning, such as "bittersweet," while a pun plays with the multiple meanings of words for humorous or rhetorical effect. These distinctions help clarify why simile is the correct answer in this context.