the.com/oxford comma

means The final comma placed before 'and' or 'or' in a list of three or more items, used to prevent ambiguity about where one item ends and the next begins.

from Named for Oxford University Press, whose in-house style guide long insisted on it; the term 'Oxford comma' itself seems to have been popularized in the early 20th century by Horace Hart's rules for Oxford printers and later by editor Peter Sutcliffe, who championed it at the Press. It's also called the 'serial comma' — the Oxford name just stuck because the university wore the habit so visibly, turning a small punctuation preference into a minor badge of institutional identity.