What makes a angel an angel, a demon a demon, and a alien a alien?

Just curious about peoples thoughts?

Mine? Well, if angels/demons are real, they could do magical shit like fly with their wings and shoot fireballs out their mouths and assholes.

If its aliens, they are using technology, like ufos to fly around.

Why the hell would angels have dicks and vaginas anyway. I never understood this part. Angels were created as gods perfect beings, and had no means to procreate.

But yet they come down to earth and magically have dicks to impregnate human women with?