The Oxford comma, (also known as the Harvard comma)

The Oxford comma (also known as the Harvard comma) refers to the comma placed before the conjunction (like “and” or “or”) in a list of three or more items. For example:

• Without Oxford comma: “I invited my parents, Shakespeare and Keats.”
• With Oxford comma: “I invited my parents, Shakespeare, and Keats.”

Both terms refer to the same punctuation rule. The name Oxford comma comes from its association with the Oxford University Press, while Harvard comma is a less common term used in the U.S., reflecting its academic usage. The Oxford comma is optional but can prevent ambiguity, making it a stylistic choice in many contexts.

https://www.grammarly.com/blog/punctuation-capitalization/what-is-the-oxford-comma