cognac

[winophite]

A while back an acquaintance of mine was talking about an aged bottle of cognac, (I don't know any details about it) someone had found and given her that she was going to try to sell. (silly girl). I asked her about it the other day, and she had come to her sences and opened it for her 50th bday. She said she still enjoys a glass of it from time to time.
My question... Is cognac a wine? and if so, does it not "go bad" a while after opening? WP