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A Voronoi cell is the generalization of a Wigner--Seitz cell for disordered structures. For a packing of monosized spheres it is the polyhedron that contains all points closer to a given sphere center than to any other. Voronoi tessellation partitions the whole space of a sphere packing into a set of non-overlapping Voronoi volumes V, which are inherently associated with the local packing density. The packing is represented quantitatively by the Voronoi volume distribution P(V). The distribution function is defined such that P(V)dV is the fraction of cells with a volume between V and V + dV.
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