A pun (also known as a pune, or a play on words) is a form of word play where a word with more than one meaning is exploited to make a joke or Riddle based on this double meaning. This can also take the form of substituting one word for a different, similarly sounding word. Usually done for humorous effect.
The problem with puns is that they are seen as the lowest form of humor (although poetry is verse), and often are not very punny, at least in English - at best, they're So Bad, It's Good. On the other hand, languages such as Chinese or Japanese, where words can be chosen for sound, character, or meaning, allow for puns of incredible complexity, working on multiple levels, and they are often viewed as an art form.
The stigma against puns in the English language is a contemporary attitude. Within historic fiction, esteemed authors pun freely, including in situations that modern tastes would regard as most inappropriate. In A Christmas Carol, Charles Dickens has Ebenezer Scrooge tell the ghost of Jacob Marley "There's more of gravy than of grave about you," and Shakespeare uses a similar pun in Romeo and Juliet where Mercutio is fatally wounded (3.1.94-95) yet plays on the different noun and adjectival meanings of grave with "Ask for me tomorrow, and you shall find me a grave man." Even prim and proper Jane Austen gives Mary Crawford the line, "Certainly, my home at my uncle's brought me acquainted with a circle of admirals. Of Rears and Vices, I saw enough," in Mansfield Park, leaving later generations of readers wondering whether Crawford is talking about different ranks of admirals or something else. Each of those examples reveals something within the larger context of the work: Scrooge puns when seeing the first ghost because he thinks the apparition is a hallucination caused by a bad meal, Mercutio is upbeat and witty concealing the seriousness of his wounds (alternatively he is panicking at having just been mortally wounded, and he is desperately trying to hide his fear with a joke), and Mary Crawford's speech foreshadows that her wealth and connections have not really made her genteel.
Puns are challenging to recreate in another language when a work is subtitled, dubbed, or translated. The translator may have to use a different example to get a pun in the new language. In some cases in novels, the translators can't recreate the pun, so they put a footnote.note
For trope names that are puns go to Punny Trope Names. For tropes that are pun names of other tropes, you want Snowclones.
