A box is placed on an inclined plane and has to be pushed down. The angle of inclination is:

The angle of repose, or critical angle of repose, of a granular material is the steepest angle of descent or dip relative to the horizontal plane to which a material can be piled without slumping. At this angle, the material on the slope face is on the verge of sliding. Since the block doesn't slide down on its own, this angle must be less than the angle of repose.