Fluid Movement

As a body travels through a fluid, turbulence may cause undesirable rotation. Consider an aircraft moving through... air.

If rotation occurs around the long nose-to-tail axis, this is called 'roll'.

If rotation occurs around the wing-to-wing axis, this is called 'pitch'.

And if the plane for some odd reason begins to spin on its vertical axis, this is called 'yaw'.

Ships have similar problems too.