This has been bugging me for a while. A greeting is a phrase you say to initiate a conversation (e.g. "Hello", "Goog morning", "Yo"), right? So what is the general term for a phrase you use to terminate a conversation (e.g. "Goodbye", "Peace", "See ya")?
In some circles, "benediction" works.
Emmett
Using that model, valediction is a more generic term for leave taking, if a bit bookish. (c.f. valedictorian, who traditionally delivers the farewell speech of a graduation ceremony.) A farewell (noun) works for me in most cases.
For a less formal option, how about a "send off"?
For a less friendly leave taking, there's a "kiss-off." I don't know where this comes from. Judas, perhaps? Grant? Martha?