This is a catch-all word to express something that's really good, pleasant, cool, etc. It can be used to describe a fancy new car, a 5-star hotel, fine looking ass, delicious food, anything really.
Example 1:
"Man this tropical resort do be bussin, they literally have everything!"
Example 2:
"Yo do you see that ass over there?"
"Yeee, that ass is bussin"
Example 3:
"Grandma's baked mac n cheese is hella bussin"