What does it mean to recoil?

Recoil refers to the action of moving back or retreating, often in response to a force. This term is commonly associated with effects such as a gun firing or an instinctive reaction to a sudden event. When something recoils, it literally gets pushed backwards as a result of some initial force, like a recoil in a firearm when it is discharged.

In the context of the choices given, the definition aligns perfectly with the concept of falling back or withdrawing. This particular movement contrasts with advancing or moving forward, which reflects progress or forward momentum, or standing still, which implies no movement at all. Therefore, understanding recoil primarily involves recognizing it as a withdrawal or retreating motion, just as indicated by the correct choice.