Velocity Storage is the name for the discrepancy between the velocity the game believes you have, and the speed your Airframe you actually expresses. Anything that prevents you from accelerating (braking shown in image) will cause this effect. Once the slowing or stopping effect ends, all (or most) of the stored velocity will be quickly expressed (as shown in the graph).

You can Velocity Store already existing momentum by simply braking. This means you can turn sharply at high speeds for minimal cost. 

You can also start a velocity storage when you are stunned (by kicking for example) as long as you were already over 50 kmh.