Phatic phrases
Phatic phrases are the phrases that follow a well-worn script, and as long as you don’t miss the beat, the words themselves don’t matter.
For example:
Hi!
What’s up?
Fine, how are you?
Not much.
Each person is responding to questions that weren’t asked, but the script is so familiar and the beats so ingrained that nobody notices.
Most greetings and sign-offs are phatic phrases. For example, the 18th C. convention of signing off with “Your obedient servant,” lacked all irony, it was merely the phatic phrase of the moment.1