Limiting force basically means the maximum or limiting value of the force, that is possible.
Eg: Consider limiting force of friction
Frictional force is a force that resists movement between two objects. If friction is limiting, it is providing the maximum possible force it can.
To physically demonstrate this, place your hand on a surface (e.g. a desk) and very lightly try and push your hand along it. You should feel a very small force (Friction) pushing back. This force is not limiting because you are not pushing hard enough. If you push your hand harder, so it moves, then you should feel a bigger frictional force pushing your hand back - and because your hand is moving, this frictional force is limiting (it is the greatest it can be for that movement).