What is a serial comma?
The serial comma is a comma that comes before the final item in a list of three or more items. It comes before the conjunction (“and” or “or”): “John, Mandy, and Lupita.” Without the serial comma, the same phrase would be “John, Mandy and Lupita.”
The serial comma is optional; different style guides have different recommendations. But most academic style guides do recommend using it consistently.
The serial comma is also called the Oxford comma or the Harvard comma.