1.nounThe act, process, method, or an instance of representing by a system or set of marks, signs, figures, or characters.
2.nounA 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)."
3.nounA specific note or piece of information written in such a notation.