Let's say you're helping a friend plan a party.

Say you're helping plan a friend's party,and he sends you a text asking you to "bring Bob, a DJ and a clown."You're pretty impressed.You had no idea Bob was so multitalented.But when the day arrives,it turns out that he's not,and you were supposed to bring three different people.As you and Bob sit at the silent, clownless party,it occurs to you that the confusion could've been avoided simply by using another comma after DJ.This final comma in a list,placed directly before the main conjunction,such as and, or, or nor,is called the serial comma,or Oxford comma.