The apostrophe ( ’  although often rendered as  ' ) is a punctuation mark, and sometimes a diacritic mark, in languages that use the Latin alphabet or certain other alphabets. In English, it serves three purposes: * The marking of the omission of one or more letters (as in the contraction of do not to don't). * The marking of possessive case (as in the cat's whiskers). * The marking as plural of written items that are not words established in English orthography (as in P's and Q's, the late 1950's). (This is considered incorrect by some; see Use in forming certain pl...