“BL” in a few sentences
“BL” stands for “Boy’s Love”, and depicts love relationships between two (or more :p) males. It’d be wrong to say they surround about gays, as BL is mostly written/drawn by female writers, and thus are idealised stories from a female point of view.
BLCDs or dramacds are audio-adaptions of existing stories. There are a few original ones out there too, but they really are in the minority. While they usually follow the manga quite accurately, they tend to cut a LOT of the original novel-versions. But the best thing about dramacds, are the seiyuu, and they are reason enough to listen to them ^^.