AKA Ass-Bandit
Why the fuck is this word used in different ways?

Here, a barbecue is food cooked quickly over high heat. In Southern US, its food cooked slowly over indirect heat or smoke. So if they're different, why use the same bloody name?

And for that matter, why the fuck did we decide that grilling should not only be used in the same way as barbecue, but to also mean cooking under direct, high heat?
I always thought anything cooked on a barbecue is a bbq.

Obviously not.
In British usage, barbecuing and grilling refer to a fast cooking process directly over high heat, while grilling also refers to cooking under a source of direct, high heat—known in the U.S. and Canada as broiling. In US English usage, however, grilling refers to a fast process over high heat, while barbecuing refers to a slow process using indirect heat and/or hot smoke (very similar to some forms of roasting). For example, in a typical U.S. home grill, food is cooked on a grate directly over hot charcoal, while in a U.S. barbecue, the coals are dispersed to the sides or at significant distance from the grate. Its South American versions are the southern Brazilian churrasco and the Argentine asado.