Any force that resists motion?
If a force F is applied on a body with mass m, the resulting acceleration of the body is is equal to a = F/m. When a force is applied on a body that is in motion, if the resulting acceleration leads to a reduction in the velocity of the body, it will ultimately come to a halt.
Unless a body is suspended in vacuum, it is in contact with other bodies. The frictional force is one that resists the motion of any two bodies that touch each other. The magnitude of frictional force is dependent on the nature of surfaces that are in contact and on the normal force between the bodies in contact. This force is one that only resists motion. There is no frictional force acting on bodies at rest and as a result it cannot initiate motion.