Base
The base is the bottom of something, in mathematics, the bottom line of a plane shape or the bottom face of a solid.
The term “base” can be used in several different mathematical contexts. It is used in the Geometry and Algebra.
Base is a side of a polygon or a face of a polyhedron, particularly one oriented perpendicular to the direction in which height is measured, or on what is considered to be the “bottom” of the figure.
Base is the surface a solid object stands on. But the top is also called a base when it is parallel to the bottom!
The prism and pyramid are named from the shape of its base
used sources – https://www.mathsisfun.com/definitions/base-geometry-.html
https://www.universoformulas.com/matematicas/geometria/tipos-prisma/