Sometimes called the serial comma. We recommend using the Oxford comma in a series of three or more terms with a single conjunction. Use a comma after the first item and in front of the conjunction:
To avoid confusion, use a comma if an item in the series requires a conjunction. If at least one item in the series already includes a comma (or if you have a series of pairs), use a semicolon as you’d use the comma, but it’d be preferable to restructure the sentence or use a list.