phatic

In linguistics, a phatic expression is one whose only function is to perform a social task, as opposed to conveying information. The term was coined by anthropologist Bronisław Malinowski in the early 1900s.

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 acknowledge the receipt of a benefit.