Coning - An unstable flight condition in which a rocket's spin causes the rear portion of the rocket to describe a circle. Coning greatly increases aerodynamic drag and reduces peak altitude.It's one of things that you'll know when you see it. I've mostly noticed it on underpowered winged rockets (e.g. an X-15). Find out more about what causes it on ROL InfoCentral.
(and, what the heck is up with my typing?)