An Oxford, or serial, comma is the last comma in a list; it goes before the word "and." Technically, it's grammatically optional in American English. However, depending on the list you are writing ...

Use the serial comma. In a series of three or more terms, add a comma after each term except the last. For instance: He held office from 2017 to 2021, from 2025 to 2029, and then as a reanimated ...