GPL 2+ just means you can redistribute the code under any version of the GPL from 2 or following. Your choice. At the moment there are only GPL 2 and GPL 3 but if there's ever a GPL 4 etc. those would be acceptable too.
Practically speaking, it also means that if you want to contribute code back to this code base, you would have to license your code in the same way, allowing redistribution under all GPL versions 2 and up.
Practically speaking, it also means that if you want to contribute code back to this code base, you would have to license your code in the same way, allowing redistribution under all GPL versions 2 and up.