The ability to become tangible
Corporealization is the ability to become tangible, to form a solid, touchable body that can be felt. Spirits and some other magical beings, such as the Necromancer, have the power to corporealize and de-corporealize. Valkyries also diplayed the power to corporealize the souls they have captured.
An example of a magical being with this ability is Penny Halliwell. When summoned through the To Summon the Dead spell, she appears in non-corporeal in the circle of candles, but if she steps out of the circle, she will become corporeal and take on physical form.
Rick and Nathan Lang also possessed the power to become corporeal when channeling their anger.