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.