Plain English Meaning

A spin the pilot did not mean to enter. The airplane stalls while the wings are not level or the rudder is misapplied, and instead of just dropping the nose, it begins rotating downward on its own.

Full Definition

An unintentional spin entry, in which an aircraft departs controlled flight and enters an autorotative, stalled descent without the pilot intending it. Typically caused by allowing the airplane to stall while uncoordinated, often as a result of distraction, divided attention, or improper rudder use during slow flight, climbs, or turns.