Splines are ridges or the teeth[1][2][3] on a drive shaft that mesh with grooves in a mating 
piece and transfer torque to this, maintaining the angular correspondence between them.
For instance, a gear mounted on a shaft might use a man spline on the shaft that fits the feminine spline on the apparatus. The splines on the pictured drive shaft match with the female splines in the center of the clutch plate, as the gear rack smooth tip of the axle is usually backed in the pilot bearing in the flywheel. An alternative to splines is definitely a keyway and important, though splines provide a longer fatigue life.[2]