From the Comma Queen at the New Yorker:
The serial comma, also known as the Oxford comma, is the one before “and” in a series of three or more: Herman Melville wrote “Moby-Dick,” “Billy Budd,” and “Bartleby, the Scrivener.”
It is also the improbable subject of a passionate debate among scholars, journalists, and copy editors. Can’t we all just get along?
Me? I use the serial comma because it creates clarity. Everything from the Comma Queen is worth your time. I have her book on hold at the library.