This expression means to be ordinary. The saying was originally a technical term in manufacturing. Here a 'run' is a spell of allowing machines to operate. The 'run of the mill' was the material coming directly from a mill without having been sorted or inspected for quality. Therefore it might include both good and inferior products. The phrase is first recorded in print in the late nineteenth century.

Übersetzung:

gewöhnlich, nullachtfünfzehn

Gegenteil(e)

The opposite of "run-of-the-mill" is "something special".

Synonym(e):

You could also say: lacking unusual or special aspects or not special in any way.