Dispersive armor was a type of armor the Klingons employed during the mid-22nd century to protect the bridges on their Birds-of-Prey. This armor was immune to the weapons of an NX-class starship.
In 2154, during the Augment Crisis, Arik Soong told Captain Jonathan Archer not to fire on the bridge of Malik's Bird-of-Prey, as its dispersive armor made it immune to Enterprise's weapons. (ENT: "The Augments")