Hidden Weapon makes the player's right-hand weapon invisible for a short time. Sheaths do not become invisible. The sorcery counts as a weapon enchantment; Hidden Weapon can thus only be used on enchantable weapons, and cannot stack with other weapon enchantments.
Hidden Weapon is mainly used in online PvP and doesn't have any real use for npcs/enemies. It is extremely useful for surprise attacks against invaders or hosts, as it makes it much harder for the opponent to block, dodge, or parry hits.