A polyhedron is a three-dimensional shape made up of flat surfaces called faces. Each face is a polygon, which means it has straight edges. Common examples of polyhedra include cubes, pyramids, and tetrahedra. The points where the edges meet are called vertices, and the lines where the faces meet are known as edges. Polyhedra can be classified into two main categories: regular and irregular. Regular polyhedra have faces that are all the same shape and size, such as the Platonic solids. Irregular polyhedra have faces that can vary in shape and size. Polyhedra are studied in geometry and have applications in various fields, including architecture and computer graphics.