Definition: The bottom of a shape, solid or three dimensional object. The base is what the object 'rests' on. Base is used in polygons, shapes and solids. The base is used as a reference side for other measurements, most often used in triangles. The base is the surface of the object that is stands on or it is the bottom line.
Examples: The bottom of the triangular based prism is considered the base. The bottom line of the trapezoid can be considered the base.