What is load angle?

In synchronous system while generator generates rated power and load increase in system, Than frequency start goes to down respectively same as rpm of the all generator start reduce but the speed of the rotating magnetic field is same, So the angle created between rotating magnetic field and generator rotor, This angle are known as load angle of generator.
(In isolated system there is same as synchronous system, Load angle very sharply increase in isolated system than synchronous system cause in the isolated system the access load share only by the particular machine while in the synchronous system there is share with all connected machine, which is very small other than)