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 called edges. Polyhedra can be classified into regular and irregular types. Regular polyhedra, also known as Platonic solids, have faces that are all the same shape and size, such as the icosahedron or dodecahedron. Irregular polyhedra have faces that can vary in shape and size, making them more complex.