It really did come from climbing and Betamax...how weird
Beta is climbing jargon that designates information about a climb. In rock climbing this may include information about a climb's difficulty, crux, style, length, quality of rock, ease to protect, required equipment, and specific information about hand or foot holds. For alpine climbs, beta may include information about the length and difficulty of the approach, availability of water on the climb and the approach, ease of exiting the route before completing it, descent information, perhaps even useful logistic information for climbs in foreign countries.
The original use of the term Beta in climbing is generally attributed to the late climber, Jack Mileski. "Beta" was short for Beta Max, a reference to an old videotape format largely replaced by the VHS format. Climbers would sometimes videotape other climbers on climbing routes, then review the tapes to evaluate techniques to help them climb the same routes in the future.
And the Lord said, let there be whitewater. So on Friday, the 13th day of the month....