Phatic

In linguistics, a phatic expression is one whose only function is to perform a social task.

For example, you're welcome is not intended to convey the message that the hearer is welcome; it is a phatic response to being thanked, which in turn is a phatic whose function is to be polite in response to a gift.

The utterance of a phatic expression is a kind of speech act.

See also etiquette.