The apostrophe is a punctuation mark, and sometimes a diacritical mark, in languages that use the Latin alphabet and some other alphabets. In English, the apostrophe is used for two basic purposes:
The marking of the omission of one or more letters, e.g. the contraction of "do not" to "don't"
The marking of possessive case of nouns
It is also used in a few exceptional cases for the marking of plurals, e.g. "p's and q's" or Oakland A's.
The same mark is used a single quotation mark. From Wikipedia
