Darkness, fog, invisibility magic, and any other effect that fully obscures a creature or object but doesn’t protect their physical form grants that creature or object concealment. Even if you have line of effect to such a target, a creature or object has concealment from you if you can’t see or otherwise observe them. You can target a creature or object with concealment using a strike, provided they aren’t hidden (see Hide and Sneak in Chapter 9: Tests). However, strikes against such targets take a bane.
Invisible Creatures
Invisible creatures always have concealment from other creatures. If an invisible creature isn’t hidden, they can still be targeted by abilities. The test made to find a hidden creature who is invisible takes a bane.