actuation force
An actuation force is the push or twist that a robot's motors and other actuators produce to make the machine move. When you bend your arm, your muscles supply the effort; in a robot, motors play the muscle's role, and the effort they deliver is the actuation force. If the joint slides in a straight line, this effort is a straight push or pull (a force); if the joint rotates, it is a twisting effort (called a torque). Engineers often lump both kinds under one umbrella name, generalized force, so a single word covers every joint whether it slides or spins.
Actuation force matters because nothing in the physical world moves for free: every acceleration, every fight against gravity, friction, or a heavy payload has to be paid for with force from somewhere. The control system's whole job, at the lowest level, is to decide how much actuation force each joint should deliver at each instant so the robot follows the path you want. Ask for too little and the arm sags or lags behind; ask for too much and it overshoots, jerks, or strains its parts. Because real motors can only push so hard, the available actuation force is a hard ceiling that quietly shapes how fast and how strong a robot can be.
A robot arm holds a 2 kg box steady in mid-air. Even though nothing moves, each joint motor must keep producing a steady actuation torque just to balance gravity's pull — let the force drop to zero and the box crashes down.
Holding still is not free: actuation force is needed even to stay put against gravity.
For a sliding joint the actuation effort is a force; for a rotating joint it is a torque. "Generalized force" is the catch-all term that covers both.