Oxford comma (serial comma)
The comma before and or or in a list of three or more.
In a list of three or more, the comma before and or or is optional. That comma is the Oxford comma (serial comma). Use it in every list, or leave it out of every list. Do not mix the two.
Examples
UseWe packed the hose, the bolt, and the wrench. (Oxford / serial comma)
UseWe packed the hose, the bolt and the wrench. (Normal comma)