Ah, it's a syrup.
Wikepedia:
Molasses or treacle is a thick syrup by-product from the processing of the sugarcane or sugar beet into sugar. (In some parts of the US, molasses also refers to sorghum syrup.) The word molasses comes from the Portuguese word melaço, which comes from mel, the Portuguese word for "honey". The quality of molasses depends on the maturity of the sugar cane or beet, the amount of sugar extracted, and the method of extraction.
I never saw this over here. We do have a syrup made from brown sugar, it's probably similar. I like it on pancakes.