There are two type of loads present on the basis of variation of 3 load parameters, which are force magnitude, direction and point of application. If all these parameter don't change with time, then it will be static load and if atleast on of them get change with time then it will be dynamic load. So fatigue is generally means continuous, that means if we continuously apply dynamic load on any body then after some cycle of load variation, body will start failing and this cause fatigue failure. Example: Fold the wire up and down continuously and then it will fail after some cycle.