It is matter, in that it behaves gravitationally the same way that ordinary matter does. (Unlike dark energy, which does not behave the same way ordinary matte

It is matter, in that it behaves gravitationally the same way that ordinary matter does. (Unlike dark energy, which does not behave the same way ordinary matter does; dark energy is actually poorly named because it does not behave like ordinary energy.) Basically, the dark matter hypothesis can successfully explain a wide variety of unexplained phenomena if there exists a substantial number of weakly-interacting, but otherwise ordinary particles.