On the good/evil axis, I see Neutrality as a state where a person is not willing to commit truly heinous or selfless acts. To a Neutral person, heinous/Evil acts (murder, torture) are unconscionable under normal circumstances, yet overly selfless/good acts (risking one's life or financial survival for others) ask too much of him. Though circumstance can potentially press him into either extreme, he doesn't normally act like a particularly good or bad person.
A Neutral person doesn't try to fight evil or commit it. He might want the forces of good to win (though if evil can offer him a better deal, he'll take it), but he won't make big sacrifices unless he needs to. He just keeps his head down, stays out of trouble, and tries to make the best of things.