This question already has an answer here:
What are the in-universe and out-of-universe meanings behind the names droids are given?
The out-of-universe origin of R2-D2 ("Reel 2 - Dialogue 2") is widely known, but what about in-universe?
There a question about the out-of-universe meaning of C-3PO as @Richard points out, but what about in-universe?
My question is different because I'm looking for a long list of in and out-of-universe info on the many droids of Star Wars.
What do they all stand for?