A pun (also known as paronomasia) is a figure of speech which consists of a deliberate confusion of similar words or phrases for rhetorical effect, whether humorous or serious. A pun can rely on the assumed equivalency of multiple similar words (homonymy), of different shades of meaning of one word (polysemy), or of a literal meaning with a metaphor. Bad puns are sometimes called "cheesy."
Walter Redfern (in Puns, Blackwell, London, 1984) succinctly said: "To pun is to treat homonyms as synonyms."
In order to be able to pun effectively it is necessary that a language must include homonyms which may readily be misrepresented as synonyms. Languages with complex gender or case structures tend not to facilitate this, although puns can be constructed in all languages with varying degrees of difficulty; i.e. puns are said to be easy to construct in languages such as Chinese or English, but rarer in Russian.
Examples:
People have a happy time vacationing in Ireland because they are walking on Eire.
Being crushed by large objects can be very depressing.
I wanted to exercise last night but it just didn't work out.