An attack or ability with the Demolition tag deals double damage to unattended objects and structures.
“Structures” include walls, doors, floors, ceilings, most forms of Difficult Terrain, and any conjured structures created by Wall spells.
“Unattended objects” includes weapons, armor, chests, cursed rings, etc. — essentially most inanimate objects that aren’t being worn or wielded by a creature.
Multiple applications of this tag to an attack or ability have no additional effect.