A pun, also called paronomasia, involves a word play which suggests two or more meanings, by exploiting multiple meanings of words, or of similar-sounding words, for an intended humorous or rhetorical effect. Puns are constructions used in jokes and idioms whose usage and meaning are entirely local to a particular language and its culture. To be understood, puns require a large vocabulary.

Example:

"Question: Why do we still have troops in Germany?

Answer: To keep the Russians in Czech" - Joke.

This joke relies on the aural ambiguity of the homophones "check" and "Czech"