What is a serial comma?

Answer 1

A serial comma is a comma used to separate a list of three or more items in a written sentence.

Yesterday I bought orange juice, bread, and yogurt at the grocery store.

A comma must be used after each object: orange juice, bread, yogurt.

A comma must be used after the last object and before "and."

Why?

The comma separates each item as a separate thing.

The comma before the "and," makes the item before it separate from the item after and.