What is the Oxford comma? Is it a comma that was educated in one of the world's most prestigious colleges?
Nope. It's the last comma in a list that comes right before the word "and."
I shall demonstrate.
"I'm going to a party with Bob, Jane, Mary, and Ted."
See that comma after "Mary?" That's an Oxford comma.
Now, there are many who would say that the placement of that comma is incorrect. In fact, if you're in England or Canada, it would be correct - they don't use the Oxford comma. (Which is odd because Oxford is in England. Whatever.)
But in the U.S., many of us (yes, I'm in this camp) believe that the Oxford comma is the way to go. It's more modern, it helps the sentence make better sense, and it makes us feel special to insist upon it.
So, unless you're in England or Canada (or one of the British protectorate countries), you'll want to go with the Oxford comma in your writing.