The halo occupation distribution (HOD) is a parameter of the halo model of galaxy clustering.[1] The halo model provides one view of the large scale structure of the universe as clumps of dark matter, while the HOD provides a view of how galactic matter is distributed within each of the dark matter clumps.[2] The HOD is used to describe three related properties of the halo model: the probability distribution relating the mass of a dark matter halo to the number of galaxies that form within that halo; the distribution in space of galactic matter within a dark matter halo; the distribution of velocities of galactic matter relative to dark matter within a dark matter halo.[3]