The difference between "vehicle power outlets" and "vehicle cigarette lighter socket?"?

I went to walmart today and was looking for a cigarette lighter splitter for my car. I want one so that I can charge my gps and listen to my ipod at the same time. I thought I had found what I needed and when I got it home, and cut open the package on the back of the device it says "use only in vehicle power outlets. Do NOT use in vehicle cigarette lighter sockets." I want to know what the difference is. I would just return it and not worry about it, accept it was in one of those impossible to open plastic packages that I sliced upon opening. Is it completely impossible to use in my cigarette lighter?