A rubric is a word or section of text which is traditionally written or printed in red ink to highlight it. The word derives from the Latin: rubrica, meaning red ochre or red chalk, and originates in Medieval illuminated manuscripts from the 13th century or earlier. In these, red letters were used to highlight initial capitals (particularly of psalms), section headings and names of religious significance, a practice known as rubrication, which was a separate stage in the production of a manuscript.
Rubric can also mean the red ink or paint used to make rubrics, or the pigment used to make it. Although red was most often used, other colours came into use from the late Middle Ages onwards, and the word rubric was used for these also.
Various figurative senses of the word have been extended from its original sense. Usually these senses are used within the set phrase "under [whatever] rubric", for example, "under this rubric, [X is true]" or "[X was done] under the rubric of Y." These senses are defined in part by Merriam-Webster's Collegiate as follows: "an authoritative rule"; "the title of a statute"; "something under which a thing is classed : CATEGORY"; "an explanatory or introductory commentary : GLOSS"; "an established rule, tradition, or custom"; "a guide listing specific criteria for grading or scoring academic [assignments] ". (See Merriam-Webster's Collegiate for the full listing.)