It means that you can lock the end point to a position and figure out the rest of the pose.
Imagine a character walking with forward kinematics. Every time you move the characters hips , you’d have to rotate the leg joints and make sure the foot doesn’t slide. Remember virtual characters don’t have friction.
IK lets you lock the foot in a spot so you can animate the body above it without having to spend time matching the foot position.
In a real world, this is like if you tried to put your hand on a door handle while jumping up and down. It’s easier to keep position when you hold the handle than if you were to just touch it.
