The pyramid has a square base from which 4 triangular faces slope upwards to meet at a single point at the top known as the apex. The apex is vertically above the centre of the square base. The perpendicular height is the height of the apex above the base.
The slant height is the height measured along a triangular face, from the middle of a base-edge up to the apex. It is the perpendicular height of that triangle, and is needed if the area of one triangular face is to be found
= one-half of base-edge x slant heightA slant edge is one of the 4 edges running from a corner of the base up to the apex, it is one of the edges of a triangular face.
The *f/b* angle is the angle between one of the triangular faces and the base. It is also known as a dihedral angle.