Rules and Methods
Let's draw another distinction. Rules, let's say, are imperatives. Roll the dice, and abide by the results: that's a rule, one basic to most tabletop role-playing. When they're well-designed, rules give a game the internal coherence that makes it a game.
Not everything you do to make a game work well is necessarily a rule, though. The looser a game is — by which I mean, the less it uses rules to proscribe play — the more inclined we are to lean on methods. By methods, I mean all of those repeatable but optional behaviors that fill the gaps left by the rules. Opting to roll the dice from a cup is a method. So is using a table to generate unplanned elements of the narrative or world.
I'd go so far as to suggest that most of what we find in the guides and rule books are better understood as methods. In practice, role-playing games tend to need fewer hard-and-fast rules than we imagine them having — particularly if we prefer to run our games like a monk. So-called “rules-lite” games demonstrate just how little is truly imperative, but much of what gets carved away the pursuit of lite-ness are the methods that keep play from bogging down in indecision.
Even games that don't present themselves as rules-lite tend to lavish more attention on some methods than others. Most games leave very little to the imagination when it comes to combat. Head into town, though, and it's easy to find yourselves staring at your character sheets while you try to figure out what's worth doing and how to make it not just playable but also interesting. Those lacunae pose less of a problem for long-time GMs than it does for a late bloomer like myself. The long-timers have a stock of methods to draw on, many of them adopted from more elaborately designed games. Me? I'm just trying to keep things from grinding to a halt.