Quadrupel

Abt, or quadrupel, is the name given to ultra-strong Trappist and abbey ales. The name Abt was pioneered to describe Westvleteren and the beer that would become St. Bernardus. Quadrupel was pioneered by La Trappe. Abts are the darker of the two, with more rich, deep fruity notes. Quads are paler, with corresponding peachy notes. Neither have much in the way of hop, and both are very strong and malty. Though both are bottle-conditioned, abts trend more towards yeast driven spice. (RateBeer)