Chocolate liqueur is a chocolate flavored liqueur made from a base liquor of whisky or vodka. One of the most common is crème de cacao, which is a light, sweet liqueur with aromatic chocolate notes (and which does not contain any cream). Other chocolate liqueurs tend to be darker and more chocolate forward.
It should not be confused with chocolate liquor, which is the unsweetened extract of the cocoa bean and is unrelated to alcohol.