CVA means "Constant Volume Adjustable". It is a bit of a misnomer because the internal volume of an oil filled shock is not constant. When the rod is retracted, the oil volume is reduced. CVA shocks compensate for this with the little hemispherical bladder inside the head end which collapses as the rod is retracted. This allows the shock to be filled without any entrained air as opposed to an emulsion style shock which has air distributed in the fluid. Generally having air in the fluid is considered a bad thing, although Tamiya offers some emulsion style shocks which cost even more than their normal shocks. The "adjustable" part of CVA refers to the fact that each shock part number has multiple lengths. The length can be adjusted by using different rod ends and different rods.
