Quote Originally Posted by The Player's Handbook 3.5e
A neutral character does what seems to be a good idea. She doesn’t feel strongly one way or the other when it comes to good vs. evil or law vs. chaos. Most neutral characters exhibit a lack of conviction or bias rather than a commitment to neutrality. Such a character thinks of good as better than evil—after all, she would rather have good neighbors and rulers than evil ones. Still, she’s not personally committed to upholding good in any abstract or universal way.
True Neutral. Perhaps the most abstract alignment of all. This description, while short, sums it up fairly accurately. True Neutral is not an alignment due to what it is - but what it is not. A True Neutral character is not going to go out of their way to help others - but they can still be loyal to their allies. I'll delve into this more in the following handbook.

What it Means to be True Neutral

Loyalty to Oneself
This is perhaps one of the most important bits. A True Neutral character is less concerned with means and ends than a good or evil character would be - it turns into less what is good and more what is right. In a world where good and evil are cosmic forces, nothing is stopping angels from being douchebags, and siding with demons being the worthwhile option.

True Neutral knows best when to fight and when to flee, and is bright enough to not die when the option to live is available.

A True Neutral character is not loyal to an external cause simply because it exists - his loyalty is earned through good times and bad - After all, A friend in need is...

... A Friend Indeed
True Neutral has the capacity to be the strongest friend you have - they aren't loyal to some esoteric cause, they're loyal to you, because you helped them. A True Neutral character isn't just some sociopathic waif who flees conflict - nor is he going to let evil stand idly by.

A True Neutral Character is loyal to his allies, and to his friends, forged by fire and ice.

Because I'm One of the Idiots Who Lives In It!
True Neutral isn't going to side with someone for an esoteric cause, like some people [glances furtively at LoyalPaladin] but are more likely to be motivated from self preservation. They don't want to disrupt the established system, but they have no special loyalty to it. Some live outside of the law, others just going about their daily lives. Moreover, they won't just let the universe end, just because of a petty grudge.