This has always been a complicated subject because of the terminology. For decades, astronomers have been aware that there is some kind of 'missing mass' out there. Some types of this 'missing mass' that are needed in the halos of galaxies may be dark, sub-luminous stars, black holes, or other under-luminous objects. But this only accounts for perhaps as much dark matter as what we already see in luminous matter. We are already dangerously close to the limit set by the cosmological abundance of deuterium. This limit says that for the present values of the Hubbel constant, matter in the 'baryonic' form of protons and neutrons cannot be more than about 10 percent of the critical density. This includes matter that has already collapsed to form black holes and sub- luminous stars.
The problem is that even more than luminous and dark baryons are needed to account for other cosmological problems. The patterns in the way that galaxies are distributed across the sky, and the various characteristics of the cosmic background radiation point towards still more gravitating stuff. Also, the recent discovery of an accelerating expansion to the universe means that there is a 'cosmological constant' or vacuum energy driving the universe. When you compare the structure to the amount of acceleration, you find that the models consistently point to 70 percent of the total 'density' of the universe as a form of dark energy, plus about 10 percent in luminous and dark baryond, plus 20 percent in some other kind of 'material' that cannot be baryons (quarks, protons, neutrons) and THIS is what we call 'dark matter' although it is not matter as we know it.