Board Thread:Wiki Discussion/@comment-24095889-20140702185358/@comment-53539-20140706094436

The "+" means "Voiceroid+". Its to separate it from "voiceroid". "Voiceroid" and "Voiceroid+" are engine versions, with the "voiceroid+" being called that because of the extras it does.

Yeah, you weren't alone with the confusion over the "+", for the first few year people didn't seem to click there was a difference at all and the +" got ignored.