Ah, the Oxford Comma. I am a devotee of this particular quirk of punctuation and, despite what followers of AP style guidelines might say about it, I am steadfast in its defense.
If you’re not a linguistics person, the Oxford (or serial) Comma is the comma at the end of a list. Take this common, and kind of jokey, example:
Oxford Comma: We invited the hookers, JFK, and Stalin.
No Oxford Comma: We invited the hookers, JFK and Stalin.
The problem with the latter is that it changes the meaning of the sentence. Removing that comma basically turns “JFK and Stalin” into a nonrestrictive appositive–there are exactly two hookers and their names are JFK and Stalin. (An example of a restrictive appositive: I have two cats, but am only taking one to the vet, so, “I’m taking my cat Fluffy to the vet.”)
The Oxford Comma is good for clarity. Some people argue that it’s not necessary because typically people will get that it’s a list, but why leave it to other people’s critical reasoning when you can just kill the ambiguity?
Embrace the Oxford Comma. It’s a beautiful thing.