Kahlua is a brand within the coffee liqueur category, founded by four friends in Mexico in 1936. The liqueur is made by combining Arabica coffee with sugar, vanilla and rum, and is used in classic cocktails such as the White Russian and Espresso Martini.
Kahlua has a flavor of sweetened coffee, with the rum adding a slight edge, but it's important to note that it also adds quite a bit of sweetness to your drink.