Question

Define the term monogram. Why are they used by artists?

Answer 1

A monogram is a character with two or more letters they use that to tell apart there work from others also to make it look unique.

Answer 2

Monogram: is a motif can be 2 or more letters (like someone's initials or signature) they are usually interwoven or combined in a decorative design, used as a logo or any other source to identify a personal possession. 
Artist use it sign their work so that people know who painted the piece.