What is Beta? It's time for some conceptual analysis here. A first try: "advice on the best way to climb a route." Not too shabby, but there is an obvious problem - you can get bad beta, perhaps beta for short people that is horrible advice for a tall (and attractive) dude like me. Alright, how about "advice or instruction on how others climb a problem?" Interesting, but you can get beta without consulting others. Imagine you are alone in the woods climbing a problem you know nothing about. You are getting stumped, but after finding a hidden hold you say to yourself "finally! I've got the beta." No one else comes into the picture here, yet you now have beta whereas before you got on the problem, you didn't.
After much thought (oh how my MA Thesis has suffered!) I think this whole business of giving a straightforward definition in misguided. Beta isn't simply a matter of information. Imagine a boulder problem with a crucial heel hook. You would never have thought to get a heel hook on that particular hold, it is around the corner and somewhat hidden, but there is a large tick mark that wraps around the arete. Based on this tick mark you make the straightforward conclusion that you should heel hook the hold. It seems to me, and I think this isn't wrong, that you haven't gotten beta on the climb simply by seeing the tick and concluding the heel hook.
Now contrast this with a situation in which there is no tick, but the person with you has been on the climb and tells you about the secret heel hook. You have clearly received beta here, but oh no! the information you've gotten is exactly the same as in the last scenario. Because of this, I find it unlikely that beta is simply a matter of information.
Alright, so our attempt at providing a definition for beta has been a failure so far. What else could it be? Perhaps "beta" is a functional notion, defined in terms of an onsight and a flash. Again then: "beta is whatever it is that precludes an onsight." Typically this will be information, but notice that on this definition, it is not solely a matter of informational content. The role that this information plays is what is fundamental, that is, information that would turn an onsight into a flash.
I've got to say, this isn't the most informative explanation. After all, we still don't know all that much about onsighting and flashing - we are still ten years away from a decent analysis of these concepts. And we can still ask, what is this mysterious thing that makes an onsight into a flash? What are its characteristics, its properties, both intrinsic and contingent. Yet after thinking about various definitions, I'm not sure we can avoid a functional analysis like this.
Look at those analytic tools you learn from philosophy! How useful, how powerful! What do others think? Sure, this is an inane waste of time, but this is the career path I've chosen, and surprisingly, this is likely the most relevant thing I've written all week. So don't knock it, play along with me here. Thought?!