AD&D alignment used to describe characters that believe that a balance must exist between law and chaos, and good and evil. It's a hard alignment to play, because it means you've always got to play for the losing side, but it's also very interesting.

I like being true neutral, but I understand that many GM's don't allow it in their games.

I found interesting the idea that true neutral is the only alignment in the end; maybe it has to do with rebellion? i.e. you choose to go against the majority. That is, in a way, true neutral.

I think that true neutral are really defined by their desire of balance, yet they find the other alignments necessary; just that they do not find correct one winning over the other.