You say Buffalo, I Say Bison

Okay, so we never really established what the hell the difference is between Buffalo and Bison, but I was pretty excited to get a chance to see these guys close up. Definitely my Yellowstone highlight.
This guy was only about 10 feet from my car door & making this gnarly snorting sound....kind of the way Zeb sounds when he snores.
We came around the corner of a tiny two lane road, and there this guy was trucking down the other side of the road.
So what do you think? Are they Buffalo or Bison?