A dark matter halo is a gravitationally bound concentration of dark matter. Its internal motions are largely supported by a distribution of particle orbits, unlike the cooling gas that can settle into a luminous galactic disk. Halo profiles, abundances and spatial correlations provide useful ingredients for modeling nonlinear clustering. The halo model uses these ingredients as an approximate statistical description of matter.[ref]
Halo Models of Large Scale Structure by Asantha Cooray and Ravi Sheth. Abstract: internal profiles, abundance and spatial distribution in the halo description
A dark matter halo is a theoretical structure that surrounds galaxies and galaxy clusters, comprising a significant portion of their total mass. Dark matter, which does not emit, absorb, or reflect light and is therefore invisible to electromagnetic observations, is inferred to exist based on its gravitational effects on visible matter.
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