An ELT Glossary : Tail (Conversational analysis)

Definition and examples : The use of a noun phrase or tag at the end of an utterance which can be  used to clarify topic and make processing easier. The tag may be :
a) A noun phrase - She's a nice girl, our neighbour.
b) A declarative verb tag - It was crazy, it was.
c) a question tag - It's hot in here, isn't it?

Further reading 

McCarthy, M. Exploring Spoken English
Paterson, K. Heads and tails

NB : Don't confuse this use of the term tail with its use in the analysis of intonation.