Jacobian IK
An inverse-kinematics method that uses the Jacobian matrix — how joints affect the end effector's motion — to iterate toward a pose.
For a chain of joints, the Jacobian matrix describes how a small change in each joint angle moves the end effector (the hand, the foot). Invert that relationship and you get a direction to nudge the angles to approach the target. Because the matrix is rarely directly invertible, the transpose, the pseudoinverse or damped least squares (Levenberg–Marquardt) are used to keep the solution stable.
Unlike CCD and FABRIK, which adjust one joint at a time geometrically, the Jacobian method solves the whole chain at once and handles multiple goals and constraints elegantly — at the cost of heavier maths per step. It is common in robotics and in animation rigging tools.