Legalism

What exactly is "legalism"? i hear that word get dropped all the time by people who are obviously criticizing something about a person or a church or a doctrine. Yet i've never been able to get a clear grasp on what exactly was being charged. Based on the word itself and the way i've heard it used, i get vague impressions though.

Does "legalism" refer to believing there are rules you have to keep to be saved? Everyone short of a universalist believes there are some rules you have to keep.

Does "legalism" refer to believing that keeping certain rules earns you God's favor? i don't think i've ever met anyone who truly believed you could earn God's favor (more to the point, a person who in their heart of hearts believed he/she was currently earning God's favor).

Does "legalism" refer to believing that even the details and minutae of God's word should be treated as essential? Why would God waste His breathe telling us those little things if it really doesn't matter whether we do them or not? And how shall we determine just which are the minutae and which are the important bits? Paul threw a fit about what a couple of guys taught about the resurrection. That sounds like minutae to me; but obviously it wasn't minutae for Paul.

Does "legalism" refer to treating trivial things as important? Well, what if whether something is trivial or important is precisely what is in question? How is it fair to charge people with "legalism" if they genuinely believe the matter they're pressing is a non-trivial matter? What should they do?--pretend like it's not important even though they believe it is?

Does "legalism" refer to inventing new rules and then binding them on other people? Well, what if whether that rule comes from men or God is exactly a point in dispute? Do the people being called "legalists" believe they just made up some rules? Or do they think those rules really are from God? If they believe a rule came from God and you don't, what does calling them "legalists" accomplish?

Does "legalism" refer to believing that if i keep certain rules better than you, then i am better than you? That's definitely pride, conceit, and arrogance; but i don't really see what "legalism" as a term contributes here.

Based on most uses of the term i've heard in my life, i gather so far that "legalism" and "legalist" practically amounts to something like "ideas which are stricter than mine" or "a person who's stricter than me." Maybe i'm wrong, but i gather that this is really more of a buzzword than a clear term which helpfully identifies something definite. What do you think?