Also known as the Harvard comma.1
In the English language, this is the comma that comes before the conjunction in a phrase that lists items serially. E.g.:
The comma just after the word "blue" is the serial comma.
- The implication here is that the comma is superfluous and snobbish.2
- I always use one, which is probably tiresome of me, but then I am superfluous, snobbish, and a holder of a degree from Harvard.3
- See! I did it again.