The short answer is: no one really knows.
To elaborate: the writing, even looking only at the official materials released by Wizards of the Coast, is wildly inconsistent and contradictory. Heck, to paraphrase something I read a long time ago, even in a single book (specifically, the 3.5 Player's Handbook) the same thing is described as being Lawful and not-Lawful in two different places. The sample Monk character is described as being intensely devoted to her martial arts forms, which is highlighted as a Lawful trait. The sample Wizard, on the other hand, is described as being intensely devoted to her arcane arts, which is highlighted as specifically non-Lawful.
So, the laws referred to by Lawful are whatever a particular player and their DM agree they are. Everything else is just varying opinions on what that agreement should look like.