End Effector

A kinematic chain is a single branch of a hierarchy used for animation with inverse kinematics (IK). The chain starts with a selected child object and travels up through ancestors until it reaches the base of the chain. The selected child object at the start of a kinematic chain is called the end effector.

Another way of looking at it is to realize that for any IK solution you explicitly move only one object. An IK solver then uses IK calculations to move and rotate all other objects in the kinematic chain to react to the object you moved. The object that you move is the end effector.