Wikipedia
Degreeting
In pragmatics, a degreeting refers to the conversational procedure by which two participants of a conversation agree to discontinue the conversation. It is so named because a degreeting concludes a conversation in a similar way that a greeting engages one.
The following conversation is an example of degreeting:
Andrew: "I'll see you later then." Bethany: "Yeah ok, see ya!" Andrew: "Bye."