I hate the term "alpha cc" since it evolved to meaning non maxis-matched cc. However, it's already set in stone - drives me nuts, but I get why it came to being called this.
Alpha refers to the alpha channels that's used, in this case to create hair (like in the sims 3) - these channels are used to determine which part of a texture is transparent or not (can be done in Photoshop). This is also how a lot of games make trees/grass. Have you ever played a game where when you turn to a certain angle the grass or some tree leaves disappear and reappear when you change your angle again - as if they have no width to them? That's flat textures using alpha channels.
Alpha doesn't mean realistic - a table or couch that has a realistic texture isn't alpha, it has nothing to do with alpha channels.
I know this term is stuck now and it most likely won't change, but hopefully some people can learn more about it. I'm sure there's a few cc creators/3D artists who cringe when they hear this term.