An "apostrophe" is a digression (veering off of the subject to talk about something else) directed towards someone or something who is not physically present.
View <http://web.cn.edu/kwheeler/lit_terms_A.html> for the full definition.
An apostrophe is a punctuation mark used to indicate either possession (e.g. Tom's car) or the omission of letters in a contraction (e.g. don't for do not).