notation

The act, process, method, or an instance of representing by a system or set of marks, signs, figures, or characters.

A system of characters, symbols, or abbreviated expressions used in an art or science or in mathematics or logic to express technical facts or quantities.

“The notations used in the two books differed. (Using notation would be incorrect).”

A specific note or piece of information written in such a notation.

“She made a notation in the margin of the book.”