From Oxford Dictionaries:
What is the 'Oxford comma'?Rumors fly around and about on the demise of the Oxford comma, but it appears that the wee mark has life, yet.
The 'Oxford comma' is an optional comma before the word 'and' at the end of a list:
We sell books, videos, and magazines.It's known as the Oxford comma because it was traditionally used by printers, readers, and editors at Oxford University Press. Not all writers and publishers use it, but it can clarify the meaning of a sentence when the items in a list are not single words:
These items are available in black and white, red and yellow, and blue and green.The Oxford comma is also known as the 'serial comma'.
From Linda Holmes on NPR:
For now, the Oxford comma lives on at Oxford. And it lives on in my heart. Life is nasty, brutish, and short (or, to introduce unnecessary ambiguity, "life is nasty, brutish and short"), and the least I can do for myself is to hold tight to the linguistic niceties about which I, for whatever reason, care. It's comforting. It's calming. And when it comes to taking a firm position about mostly unimportant debates, that's about all I can hope for.The Oxford comma lives on in my heart, too, and I will continue to place the mark in a series. Even if the comma dies, I will flog the poor creature for my personal use, so long as I live.