Crème de Moka is an early style of coffee liqueur.
Martin's Menu Dictionary, from 1901, describes it as a liqueur from "coffee and bitter almonds", while Duplais's Treatise on the Manufacture & Distillation of Alcoholic Liquors gives a recipe that is simply alcohol, sugar, and coffee. The latter style is more frequently encountered in modern reconstructions of the beverage.
The term "Moka" refers to the port of Mokha, in modern Yemen, which was the major port for export of coffee from Ethiopian and Yemen to external markets, due to Ottoman restrictions on trade from other ports.