The term repulsive dark matter (sometimes abbreviated RDM) refers to a dark-matter concept that is repulsive in such a way that its density is limited. It is presumed to be some type of particle that interacts by gravity, but some other force keeps particles of that type from being too close to each other. The concept is motivated by models such as cosmological simulations that reflect many of the observed characteristics of the universe, an exception being that the dark matter in these models gathers in such a way to produce more dwarf galaxies and cause galaxies have more central mass and gravity. If dark matter resists high density, more observational data could be explained with only this change to the cosmological models that appear to be otherwise working.
The concept of repulsive dark matter has been explored theorizing different kinds of forces, probably since cosmological simulations began to show the discrepancy. Fuzzy dark matter (FDM) falls under this class of dark matter theories and the term ultralight repulsive dark matter has been used for the concept.