Speed Wobble
Also known as: wobble, wobbles
Uncontrollable side-to-side oscillation of the board when you pick up too much speed.
Extended definition
Speed wobble is that violent shimmy that shows up bombing fast: the board starts zigzagging on its own and, if you don't kill it by relaxing your body and lowering your center of gravity, it ends in a slam. It usually comes from bushings that are too soft, loosely set trucks or tension in your legs. It's typical in downhill, longboard and long descents; its extreme version is the death wobble.