If you were to plot a speed torque graph, a motor will operate in the top right hand side.
That would be single quadrant.
If the direction was to change, so same torque, but motor reversed, i.e. negative velocity, it would be 2 quadrant drive.
As this is a VFD
, the motor can actually dump power into the VFD, which mathematically means the lower 1/2 quadrants are also occupied. Hence you would have a 4 quadrant drive.
Difficult to describe without drawing paper.