The Wigner-Seitz cell is the Voronoi cell of a lattice point — it contains all points closer to that lattice point than to any other. Explore 2D Bravais lattices and their first Brillouin zones.
The Wigner-Seitz cell (direct space) and the first Brillouin zone (reciprocal space) are both Voronoi cells — of the real and reciprocal lattice respectively. In condensed matter physics, the Brillouin zone is fundamental to understanding electronic band structure (Bloch theorem).