Can you please explain aircraft spin in simple non-mathematical terms?
A spin is a kind of aggravated stall in which one wing becomes more stalled than the other one. This imbalance in lift results in an autorotative motion abound a vertical axis, generally passing through the inboard wing of the aircraft. Spins can be initiated be stalling the airplane in a uncoordinated turn, which causes the inboard wing to enter a deeper stall than the outboard wing. An airplane must always 1) be in an aerodynamic stall in 2) uncoordinated flight in order to enter a spin.
The simplest answer may be: An airplane spins as a result of being uncoordinated when a stall occurs. Uncoordinated means the nose and tail of the airplane are not inline with the flight path. So if the airplane is moving in one direction, but the airplane is pointing in another direction, then it is likely to spin in the event of a stall. That is the simple explanation. The deeper life saving explanation is contained in the video linked here.
This video explains common false notions about how an airplane works that can cause a pilot to stall and spin his or her airplane. Understanding these can help keep you safe when flying. Covered is the skidded turn which is the most common cause of spins. There is some math on how to calculate stall speed for various bank angles, but you can just skip over it if you are not interested. Please let me know if you have questions after watching.