Serial comma

The serial comma or Oxford comma is a comma used directly after the second-to-last item in a list of three or more items. For example, a list of three people may be shown as "Alice, Bob, and Charlie" (with the comma) or "Alice, Bob and Charlie" (without the comma).
Some style guides prefer using the comma, while others advise against it. It may sometimes be useful to add the comma to avoid confusion. For example, a sentence such as "Please bring Marcus, a musician and a skater to the dinner event today" may confuse anyone reading that sentence. Without the Oxford comma, they might think that Marcus is a musician and a skater, so they would need to bring Marcus instead of three people to that dinner event today.
When following a style guide that opposes the comma, one can rearrange the terms to avoid confusion. For example, saying "a musician, a skater and Marcus" does not change the intended meaning, but it avoids the confusion.