What does BC<number> stand for in image formats?

I was scrolling trough the formats and I saw this BC part. To be specific I saw it in VK_FORMAT_BC1_RGB_UNORM_BLOCK so the “BC1” part.
From descriptions I am guessing it has to do with compression but I can’t figure out what it is supposed to mean or stand for.

I don’t want to look like a jerk, but…

Ooh… lol thanks… sometimes my brain refuses to think logically. xD

While being jerks, there’s also a manual: