INTRODUCTION
The figures such as triangles, rectangle, squares, circles etc. which have only two dimensions, namely length and breadth are called plane figures or 2-dimensional figures.

The figure such as cube, cuboid, cylinder, pyramid etc. which have three dimensions namely length, breadth & height are called solid figures or 3-dimensional figures.

Types of Solid
There are mainly three types of solids :
(1)     Prism :  A solid whose top and base are identical polygons and side faces are rectangles, is called a prism. In a square prism whose top and base are congruent squares. (2)     Pyramid : A solid whose side faces are triangles and base is any polygon is called a pyramid. Figure shows a pentagonal pyramid. (3)     Sphere : Sphere is a solid whose every point is equidistant from a fixed point. Figure shows the sphere. Note : (i)     All the side faces of a pyramid (squares, rectangular, triangular, pentagonal etc.) are triangular.
(ii)     A  pyramid is named according to the shape of its non-triangular face. If all the faces are triangular, then it is called a triangular pyramid or tetrahedron.