The 5 distinct 2D lattice types — all periodic crystal structures reduce to these
Bravais lattices are the 14 (3D) or 5 (2D) distinct ways to tile space with a periodic array of points, classified by their symmetry groups. Every crystal structure is a Bravais lattice plus a basis (atoms within the unit cell). The Wigner-Seitz cell is the primitive unit cell constructed by Voronoi tessellation — the set of points closer to the origin than to any other lattice point. In reciprocal space, the Wigner-Seitz cell of the reciprocal lattice is the first Brillouin zone, the fundamental domain for electronic band structure.