Run-of-the-mill means perfectly ordinary, nothing special. A run-of-the-mill job, run-of-the-mill stuff, nothing run-of-the-mill about it.
It is mildly dismissive without being rude, since run-of-the-mill says adequate rather than bad. The phrase dates from 1922 and comes from the uniform output of a mill before any sorting.
1adjectiverun-of-the-millPerfectly ordinary; nothing special.
“It was just a run-of-the-mill hotel, clean enough but with nothing memorable about it.”
run-of-the-mill is a quality.
From 1922, from the uniform output of a mill before it has been sorted by quality.
From 1922; from the fact that product produced by a mill should be uniform and like that of any other similar run.
Etymology from Wiktionary, CC BY-SA
Practised in Idioms