What does 'orbital' mean when speaking wheels? I want to build my own dirt jumper, mostly using Octane One parts. At this site, there's two versions of the wheel. An 15mm orbital and an 20mm orbital. What is the difference, and which is the most common?

Orbital is the brand name of the hub. 15mm and 20mm are different axle diameters, get the one that matches your fork.

Edit: Most dirt jumping, DH and freeride forks use 20mm, 15mm is a newer standard used mostly for cross country.