run of the mill

run-of-the-mill

Common, standard, or average; mediocre. It was a run-of-the-mill action movie—fine to kill a couple hours, but nothing special. I must say, for how many interesting points you bring up in class, your paper is rather run-of-the-mill.
Farlex Dictionary of Idioms.

run of the mill

Ordinary, average, as in There's nothing special about these singers-they're just run of the mill. This expression alludes to fabrics coming directly from a mill without having been sorted or inspected for quality. It has survived such similar phrases as run of the mine and run of the kiln, for the products of mines and kilns. [Late 1800s]
See also: mill, of, run
The American Heritage® Dictionary of Idioms by Christine Ammer.

run of the mill

the ordinary or undistinguished type.
In this expression, the run is literally the material produced from a mill before it has been sorted or inspected for quality.
See also: mill, of, run
Farlex Partner Idioms Dictionary

run of the mill

An ordinary, uneventful sequence of events. The run in this term refers to a mill’s average output, before it has been graded or sorted. Also stated as run of the mine or the kiln, these terms come from the late nineteenth century. They began to be used figuratively in the twentieth century, as in “A darned sight better-looking than the run of the mill wives” (Hearst’s International, 1930). It is also written run-of-the-mill.
See also: mill, of, run
The Dictionary of Clichés by Christine Ammer
See also:
  • run-of-the-mill
  • not anything to write home about
  • not something to write home about
  • not worth writing home about
  • gin mill
  • palace
  • be in at the kill
  • grist to the mill
  • pass in a crowd
  • so-so
References in periodicals archive
Formerly trained by Dermot Weld in Ireland, some of his form is plenty good enough to take a run of the mill all-weather maiden.
The WORST releases of the week Siskin - Surrender They may be classically-trained, butWest Yorkshire lass Kirsty Newton and Spain-born Galen Ayers must have missed the class on what makes run of the mill into something special.
Read into that what you will, but as it features a military choir and Hungarian orchestra, don't expect it to fit in the box marked run of the mill.
There are run of the mill performances (Come On England), dreadful mistakes (Stand Up 4 England), ugly fouls (Hey Baby) and red card offences (Sing It For England).
The pubs are the Bridal Path, Whickham; Queen's Head, Winlaton; Crown and Cannon, Winlaton; Huntsman, Blaydon Bank, and the Run of the Mill, Winlaton Mill.