He doesn't use the word, but what he's talking about is an honor code, an inflexible and sometimes even fatal set of rules that must be followed regardless of the circumstances for no very clear reason other than a sense that it's expected.
The question is, expected by whom? In modern-day societies with honor codes (such as highland Albania with it's “Kanun of Lek”), the code is enforced by the expectations of the community. As an Albanian highlander, you might not have liked your cousin, you might not even have known him, but according to the rules of the “Kanun of Lek,” you must avenge his death. If you fail to do so, the other villagers will see you as a man of no consequence, a non-entity, easy prey.
The world of noir, though, is amoral. Moral men like Sam Spade are always in a minority of one. There is no village, and no one who will judge that you have “lost your honor” if you don't avenge your partner. No one will even care. Sam Spade destroys his own chance at love and happiness for fear of a judgment that doesn't exist in the first place. That's the tragedy of honor in noir.