I was going to write another one of my usual posts, grabbing quotes from throughout the thread and responding to them specifically. However, instead I've decided to go back to the titular question: What is a rogue to you?
A rogue to me is the guy who doesn't play by your rules.
He's Han Solo. Indiana Jones. Other characters not played by Harrison Ford. The Dread Pirate Roberts. Captain Blood. Some variations on Robin Hood. Bilbo Baggins. Mat Cauthon. Catwoman. The Black Cat. Bond... James Bond. The Doctor. Batman.
He's a liar and a cheat and the most trustworthy person you know.
He sneaks about in shadows and stands out in a crowd.
If he wanted your stuff he'd already have it.
I categorically reject all suggestions he should be weak in combat. Nonsense. There's two types of adventurers that aren't that great in combat: low level ones and dead ones. If you want to roll up a character that sucks in combat, more power to you. Just don't go saddling any classes in my Player's Handbook with mandatory incompetence.
Is he the toughest guy around? No.
Does he use big weapons or wear shiny armour? No.
But he's probably not tied down to your ideas of what a fair fight are. His idea of a fair fight is the one where he walks away without a scratch while you and yours lie dead and dying.
He might do it through being stealthy. He might do it through relying on a little help from his friends, catching foes who are distracted. He might do it by making you underestimate him. He might do it by just being that good and that fast. When he's really on his game, he just might trick you into doing it to yourself.
It shouldn't be called backstab. It shouldn't be called sneak attack. It's "Catch them with their pants down". It's "Mock them until they forget to defend themselves". It's "Bring a gun to a sword fight". It's "Shoot them under the table while they're still busy uttering threats".
He can deal with traps, climb walls, and pick locks. He can do these all well, he might even be the best, but he's not the only one who can do them. He never was.
Locked doors, traps, pockets that need picking and walls that needed climbing all predate the introduction of the Thief class. They still occur in campaigns where nobody plays a Thief or a Rogue. The idea that only one class should be good at these things is rubbish, as far as I'm concerned.
No class should (or even reasonably could) be dominant in all aspects of any area of the game. Everyone should be able to contribute meaningfully in combat, exploration, and social interaction. Each class should do so in ways that suit that class.
A rogue should be able to be roguish in all things. Combat, exploration, and social interaction. He should be able to distract you, charm you, intimidate you, manipulate you, mislead you, and catch you off your guard. He should climb walls and social ladders. He should be able to escape traps, disarm traps, and set traps, including verbal ones.
That's what a rogue is to me, anyways.