A numeronym is a number-based word.
Numeronyms date back to the 1980's in an effort to shorten lengthy words. The first use of a numeronym is credited to Digital Equipment Corporation (DEC), a former computer company purchased in the 1990's by Compaq, where an admin utilized this technique to shorten employee Jan Scherpenhuizen's long last name for an email account with the handle "s12n".
Though initially a joke, it took flight and by 1985 the company was using the method for the word "internationalization" (i18n).
Numeronyms don't always take the same format. K9 is a Numeronym for canine. 101 is typically used for an introductory course.