There are 31 questions tagged with the alpha tag, a lot of which are also tagged transparency. Most of these are basic questions about transparency, with only a few about advanced manipulation of alpha channels. The tag alpha does not have an explanation.
I vote to make alpha a synonym of transparency and add a mention about alpha channels in the transparency description.
I will add two answers to guide the voting process. Upvote the one you agree with. There is no need to downvote an answer.