The figure shows a prismatic bar whose right end is an inclined plane. The loads on either end have magnitude P and are directed leftwards and rightwards respectively. The t axis is taken along the inclined plane and the n axis is taken perpendicular to it. The angle between the n axis and the horizontal x axis is theta. The projection of the force P along the n axis is N.   

The perpendicular component (acting in the n direction) is termed the normal force N:
N=P cos θ