Crème de cacao is a cacao (chocolate bean) flavored liqueur, often scented with vanilla. It is different from chocolate liqueur, which is usually sweeter and more syrupy.
It exists in two different variations: Dark crème de cacao is dark brown, while White crème de cacao is a clear, colorless form of the same liqueur.
If a recipe calls for just crème de cacao, the white variant is usually the correct to use.