The serial comma, also called the Oxford comma, comes before the final and or or in a series of three or more items. In We packed a map, a flashlight, and a spare battery, the comma after flashlight is the serial comma.
When the comma helps
The program thanks the founders, Mira Patel and Leo Chen. can mean that Mira and Leo are the founders or that they are two additional people being thanked. If they are additional people, The program thanks the founders, Mira Patel, and Leo Chen. makes the three entries clearer.
Style and clarity
Some editorial styles use the serial comma routinely. Others omit it in simple lists and add it when it helps readers. Follow your style guide. If a list still seems ambiguous, you can change the order or make the relationship explicit. If Mira and Leo are the founders, write The program thanks Mira Patel and Leo Chen, who founded it. For commas outside lists, see comma.
