The word “fifteen”, the Arabic numeral “15”, and the Roman numeral “XV” are all numerals representing the number fifteen.
2002 — Laurie Bauer & Rodney Huddleston, "Lexical word-formation", p1621-1722 in The Cambridge Grammar of the English Language, p1715
We use the term numeral for linguistic expressions and number for meanings. For example, five is a numeral expressing the number "5" - and fifteen hundred and one thousand five hundred are different numerals expressing the same number, "1,500".
