Unplugged and acoustic is the same. Unplugged is just the name of the show from MTV where they show acoustic concerts. The people use it now when they talk about acoustic shows.

Prayer 94 ist not acoustic /unplugged but electric.

I think Becky is right. Originally they wanted to make an acoustic-album but when I read the press releases and stuff I'm not that sure that it will be acoustic but new versions of the songs.