Service Level Agreement
Also known as: SLA, response time promise
A written promise about how fast you will respond and what you will fix, so neither side is guessing.
A service level agreement is short and specific. How quickly you answer, which hours count, what counts as urgent, and what is not included.
Clients ask for this far less than they should, which is why offering it unprompted makes a small shop look like a serious one.
Only promise what you can keep on your worst week. A promise of two hours that you meet most of the time is worse than a promise of one business day that you always meet, because the first one trains the client to check on you.