Living Weapon is a keyword ability.
It is found on Artifact Equipment cards introduced in the Mirrodin Besieged Set. When a card with Living weapon enters the battlefield, it puts a 0/0 black Germ creature token into play and attaches itself to it. Living weapons are themselves creatures until they die or their controller chooses to equip it to a different creature, When the equipment is detached from the Germ it dies as it is now a 0/0 creature. Due to state-based effects it is put into the graveyard and ceases to exist.
702.91. Living Weapon
- 702.91a Living weapon is a triggered ability. “Living weapon” means “When this Equipment enters the battlefield, put a 0/0 black Germ creature token onto the battlefield, then attach this Equipment to it.”