What is Guinan?

Guinan's true nature is never revealed. We only know that she has a number of superhuman abilities.

From TNG: "Q Who?":

Picard and Q are seated by one of the front windows. Guinan comes over. Q immediately stands and backs off like a man about to be physically attacked.

"You! "

"None other. "

"Picard, if you had half the sense you pretend to have, you would get her off your ship immediately -- and if you like I will be more than pleased to expedite her departure. "

Picard looks to Guinan.

"You know him. "

"We had some dealings. "

"Those dealings were two centuries ago. This creature is not what she appears to be. She's an imp -- where she goes trouble always follows. "

"You're speaking of yourself, Q -- not Guinan. "

"Guinan? Is that your name now?"

So, let's review some of Guinan's background:

So what is Guinan?

Some sort of transcendent El-Aurian, sort of like Wesley Crusher being a transcendent human who became a Traveller? They had the beginnings of Q powers.

Is she a rogue Q who left the continuum like Quinn and the parents of the girl in TNG: "True Q?"

Or is she of some yet unidentified species perhaps even more powerful then the Q who simply poses as an El-Aurian and human in order to speed along their developement or for some more sinister purpose we don't know about yet? While Guinan always appeared benevolent to me, I've also never seen any species that scared a fully-powered Q before.

And while Q is known as the "God of Lies" to some species, I've never known him to really lie to Picard before. Held back information, yes, exaggerated a bit, perhaps, but flat out lied? Not that I recall. So is what he is saying that she is dangerous accurate? I wish they had followed up on those earlier implications further.

(Theory by Bond, James Bond)