You'll often see a rubric used in academia as a guide listing specific criteria for grading or scoring academic papers, projects, or tests. But the word rubric has at least three other applications and an interesting origin.
It can mean: a heading on a document; a direction in a liturgical book as to how a church service should be conducted; or a statement of purpose or function.
The word rubric has origins in late Middle English rubrish which was the original way to refer to a heading, section of text. Earlier Old French rubriche had the same meaning and came from the Latin rubrica.
Rubrica was a color designation for terra, to describe both a red clay or ink in the red ocher/ochre color.
Medieval printers had few ways to give emphasis to text on headings and the first character of a paragraph. Illuminated manuscripts could be quite elaborate and beautiful, but fonts were not standardized and there was no italic or bold. That left them to use color for emphasis.
Ochre is a naturally occurring pigment from certain clay deposits containing iron oxides, and has been used since prehistoric times to give color to dyes, paints and inks. Ochre colors are yellow, brown, red and purple. The most common in printing colored text was red ochre. In Latin, red ochre is rubrica and that is the origin of the word rubric as these red emphasized headings. Scholars who penned manuscripts in red ink were known as rubricians.)
This was taken further in the many religious texts that were reproduced. Those texts, used by clergy, included a kind of "stage directions" for the clergyman who was reading. These directions were printed in red while the text for the congregation was printed in black ink. This gave an additional meaning to the red rubric writing as instructional text.
As universities were created and books became more commonly used, scholars grading student papers would use red ink to leave instructions, suggestions and corrections on student papers. The practice has survived, although in some educational settings using red ink is now frowned on as being too negative. personally, I find criticism the same in any color.
An earlier version of this post appeaed on my blog Why Name It That?