The Oxford comma, sometimes called the serial comma, is the one that comes after the next to last item in a list. It’s followed by and or or, and then the last item in the list. Or does it? This is one of the Great Debates among grammarians.
In school, I was taught that and or or took the place of the comma. And some still say that. Magazines and newspapers, for instance, don’t use the Oxford comma. But if you’re writing a paper for school, you’ll get points off if you don’t use it.
The answer is, it depends on which style book applies. Chicago styles is the best known and most often used style, but it’s not the only one. AP Styles is the one newspapers and most magazines use. So, the answer to whether or not to use it is: It depends on which style you are writing in. At school, for instance, they’ll probably tell you to use MLA Styles, which is similar to Chicago. It you’re just writing for yourself, if you’re not being held to a style or graded, you get to choose. Neither is right and neither is wrong.