Newton's Third Law states that for every action, there is an equal and opposite reaction. This means that when one object exerts a force on another object, the second object exerts an equal force back on the first object, but in the opposite direction. These forces always occur in pairs and act on different objects.

If object A exerts a force on object B, object B must reply with a force of equal size and in the opposite direction, according to Newton’s third law of motion.

This law illustrates nature's symmetry: forces always exist in pairs, and one body cannot exert a force on another without also being subjected to one. This law is sometimes referred to as action-reaction, with the action being the force exerted and the reaction being the force received as a result.