The action force in Newton's Third Law of Motion doesn't have a specific name. It's just referred to as the action force. The important thing is that it always has an equal and opposite reaction force.

Here's how it works:

* Action Force: This is the force that one object exerts on another object.

* Reaction Force: This is the equal and opposite force that the second object exerts back on the first object.

For example, if you push a wall (action force), the wall pushes back on you (reaction force). This is why you feel the wall pushing against your hand.

So, to answer your question, the action force is simply the force that initiates the interaction between two objects. It's the "cause" of the reaction force.