A measure of a projectile's ability to coast. It is defined as Cb = M/CdA where M is the projectile's mass and CdA is the Drag Form Factor (q.v.). At any given velocity and air density, the deceleration of a rocket from drag is inversely proportional to this value. Intuitively, it is the principle behind why a tightly crumpled piece of paper can be thrown farther than a loosely crumpled one.