As obvious as it may seem, Dark Matter is Dark Matter. It is matter that doesn't interact with light and accounts for most of the gravity we see

The science goes a tad deeper than that. We have a fairly complete model for the interactions involving matter we can see, and none of that kind of framework for DM. We know some things about what DM isn;t, in terms of the standard model, but we still don't know what it is (in a physics sense)