A measure o' a projectile's ability t' coast. It is defined as Cb = M/CdA where M be t' projectile's mass and CdA be t' Drag Form Factor (q.v.). Blimey! Blimey! At any given velocity and air density, arrr, t' deceleration o' a rocket from drag is inversely proportional t' this value. Avast, me proud beauty! Blimey! Intuitively, it be t' principle behind why a tightly crumpled piece o' paper can be thrown farther than a loosely crumpled one.