A dark, very rich, complex, very strong Belgian ale. Complex, rich, smooth and dangerous.
Authentic Trappist versions tend to be drier (Belgians would say "more digestible") than Abbey versions, which can be rather sweet and full-bodied. Higher bitterness is allowable in Abbey-style beers with a higher FG. Barleywine-type beers (e.g., Scaldis/Bush, La Trappe Quadrupel, Weyerbacher QUAD) and Spiced/Christmas-type beers (e.g., N'ice Chouffe, Affligem Nöel) should be entered in the Belgian Specialty Ale category (16E), not this category. Traditionally bottle-conditioned ("refermented in the bottle").
Westvleteren 12 (yellow cap), Rochefort 10 (blue cap), St. Bernardus Abt 12, Gouden Carolus Grand Cru of the Emperor, Achel Extra Brune, Rochefort 8 (green cap), Southampton Abbot 12, Chimay Grande Reserve (Blue), Brasserie des Rocs Grand Cru, Gulden Draak, Kasteelbier Bière du Chateau Donker, Lost Abbey Judgment Day, Russian River Salvation
You can view the complete style details on the BJCP website. The 2008 style guide is obsolete but there is a similar 2015 style that you can view below...