In many Adventure Paths or specific books I find this "Elite" sorta template on creatures, but if memory serves me I've never actually found descriptions about what's the difference between a standard creature and an elite one. So that's the question, what is the difference between a standard creature and an elite one?
"Elite" isn't a template the way that Lycanthrope and Half-Fiend are. Rather, "elite" is a descriptor, to indicate that the described creature is somehow a cut above the rest of their kind. In my experience, they're typically used as mini-bosses, squad leaders, etc..
There are two major ways I've found recently that a creature can become elite: the addition of class levels (eg., the Elite Kobold gains 4 levels of Warrior) or fiat (eg., the Elite Bronze Giant is just a Bronze Giant with some tweaked stats and default gear). I seem to recall seeing some Elite creatures that had additional racial HD, but I'm not finding them at the moment; it's probable that that was more of a D&D 3.0/3.5 thing.