Oh, it can be those too (though...bbq fish? weird). BBQ, to me, refers to preperation, not meat type. I just don't like the vinegary Eastern style.
BBQ is preperation? Well... sort of. There are three or four main ways of BBQ'ing:
Grilling over Direct Heat (typical hambers and hot dogs-type, includes some ways of preparing ribs, brats, etc.)
Grilling over Indirect Heat (more of a radiant heat)
Smoking (Heat provided by radian heat, but with smoke)
Then there is Rotissire which is its own sort of critter
If you aren't doing fish, you are missing out! Grilled Tuna steaks, Smoked Salmon, Cedar planked salmon, Grilled Trout w/ bacon... Even oysters and mussels are great for BBQ.
Now, if you mean BBQ is based upon a BBQ sauce... well, I'll respectfully disagree.