A scotch whisky
that has been aged in the barrel at least 12 years.
Aging of Scotch takes place in an oak cask, which is charred inside before being filled. Over the years, the whisky seeps in and out of the charcoal. This filters it, mellowing it, and gives it the caramel color (charred wood, like charred sugar, produces caramel, both being of similar chemical composition.)
Once the scotch is bottled the aging stops.
If you have a bottle of scotch which was distilled in 1944 and bottled in 1956, you have a bottle of 12 year old scotch.
When my roommate from college came to town we reminisced over a bottle of 12 year old.