chronic is a strain of weed, but its mostly just used as slang (bud, kind, grass, pot, herb, weed, maryjane, sweet sweet chiba, etc.) KB is short for kind bud (I think, might be something else where you are) kind bud is so called because its typically quite good.

best advice I can give, don't buy weed based on what the dealer calls it. buy weed based on your own observations, i.e. smells good, dry, crystals etc. best way to find out though, is to SMOKE IT! woo! smoke it up! all of it, smoke it to your head!