Here's how it's stated:

* For every action, there is an equal and opposite reaction.

This means that when one object exerts a force on a second object (the action), the second object exerts an equal and opposite force back on the first object (the reaction). These forces always occur in pairs and act on different objects.

Examples:

* When you push against a wall, the wall pushes back on you with an equal force.

* When you jump off the ground, your feet exert a downward force on the ground, and the ground exerts an upward force on your feet.

* When a rocket engine expels hot gas downwards, the gas exerts an upward force on the rocket, propelling it upwards.