A spin is a yaw aggravated stall which results in rotation about the spin axis. The aircraft follows a steep, "corkscrew" like, downward path.
Spins can be entered, either intentionally or unintentionally, from any flight attitude and at practically any airspeed. If a stalled aircraft is subjected to a sufficient yaw rate, it will enter a spin. The yaw can be induced by improper use of the rudder or can be a result of the wing drop characteristics of the aircraft in question. In a spin, both wings are in a stalled condition but one wing will be in a deeper stall than the other. The drag is greater on the more deeply stalled wing causing the aircraft to autorotate (yaw) toward that wing. Spins are characterised by high angle of attack, low airspeed and high rate of descent.
A specific and often counter-intuitive set of actions may be required to achieve a successful recovery from the spin. If the pilot uses incorrect technique or if the aircraft exceeds spin certification limitations or if the aircraft is improperly loaded (beyond aft centre of gravity limitations), the spin is likely to result in a crash.