What does "tangential" mean?

Tangential: Of or pertaining to a tangent; in the direction of a tangent. Tangential force (Mech.), a force which acts on a moving body in the direction of a tangent to the path of the body, its effect being to increase or diminish the velocity; -- distinguished from a normal force, which acts at right angles to the tangent and changes the direction of the motion without changing the velocity. -- Tangential stress. (Engin.) See Shear, n., 3.