Meaning: Something is run-of-the-mill if it is ordinary and nothing special.
•There wasn’t much on TV so we just watched some run-of-the-mill old cowboy movie.
•I don’t know why he won the competition. He wasn’t terrible, but he wasn’t anything special either; just a run-of-the-mill singer as far as I could see.
Origin: A mill is a building in which machinery makes products, like a factory. The phrase “run of the mill” first referred especially to machine-made clothes, which were seen as less “special” than hand-made clothes. The phrase than began to be used idiomatically to describe anything that was not special, but was a standard or typical example of something.