What does seamless transformation mean in 3D animation?

IK-FK seamless transformation, in the field of three-dimensional animation, IK is called reverse dynamics, FK is forward dynamics, and it is only the setting of three-dimensional model to limit the movement of bones, but IK and FK cannot exist at the same time and can only be transformed into each other. Seamless transformation means that when using IK to limit the spatial position of bones, you want to switch to FK adjustment, but the spatial position of bones will not change, and the animation trajectory adjusted with IK can be adjusted with FK. The perfect combination is basically seamless, that is to say, IK-FK can be switched at will in an animation without affecting animation fluency and animation trajectory deviation.