Interactive IK and Applied IK are alternative methods to the IK Solver methods.
With Interactive IK and the Auto Key button turned on, you position your model on keyframes, and the IK solution is interpolated between those keyframes. Because the IK solution accounts for multiple objects and the joints between objects, the interpolated animation of an IK object is usually different from the animation of objects without IK.
Applied IK requires you bind one or more parts of your IK structure to animated follow objects. Once bound, you can select any object in your kinematic chain and click Apply IK. This calculates the IK solution for each frame of the animation and places transform keys for every object in the IK chain.