serial comma

:  a comma used to separate the second-to-last item in a list from a final item introduced by the conjunction and or or If you've always used the serial comma—“red, white, and blue”—its absence can look slipshod and lazy. If you were taught the more streamlined AP style—“red, white and blue”—the extra comma may seem fussy and pretentious. — Jan Freeman, Pittsburgh Post-Gazette, 3 Apr. 2011 —called also Harvard comma, Oxford comma