This is a really funny example regarding the value of the Oxford comma. Surprisingly, there is much debate about whether this comma is useful.
The actual name is called a serial comma because it is used before “and” in a list (or series). It is commonly referred to as the Oxford comma because the Oxford University Press recommends its use.
The flag is red, white, and blue.
The comma after “white” and before “and” is the Oxford comma.
I personally always use it to add clarity (as in the instance above). Others arguing against the comma say that it’s redundant because the commas preceding the Oxford comma are used to replace the word “and.”
“The flag is red, white and blue” is used as opposed to “The flag is red and white and blue.” In the first sentence, the comma after “red” takes the place of “and” while the “and” after “white” stays the same.
I hope I’ve made this argument clear. If you still have questions, just leave some in the ask box!