Single barrel whiskey is amongst the rarest of any spirit from America. The term refers to whiskey which has been aged in a single barrel, and has been bottled unblended (thank you Captain Obvious). These are also often bottled at natural cask strength "straight from the barrel", and because they are unblended they usually offer an unbridled level of richness and complexity, and are held in a special place by connoisseurs of bourbon and other whiskeys.