Question Tag

A question tag or tag question (also known as tail question) is a grammatical structure in which a declarative statement or an imperative is turned into a question by adding an interrogative fragment (the "tag"). For example, in the sentence "You're John, aren't you?", the statement "You're John" is turned into a question by the tag "aren't you". The term "question tag" is generally preferred by British grammarians, while their American counterparts prefer "tag question".

http://en.wikipedia.org/wiki/Tag_question