Coffee liqueur is a type of liqueur flavored with coffee beans and, sometimes, other herbs and spices. While coffee liqueur is often homemade, there are many commercial brands, which offer a wide variety of base spirits, bottling proofs, and flavor profiles.
Kahlua, Kamora, and Patron Cafe are common brands of coffee liqueur. Kahlua is rum based and not only makes an "Especial" version which is higher proof and uses better coffee beans, but also flavors such as vanilla, mocha, hazelnut, and peppermint mocha, which mimic popular coffee creamer flavors. Patron Cafe, not surprisingly, is tequila based.
In smaller, more regional brands, Firelit produces a coffee liqueur with coffee from small, quality oriented roasters, and matches the flavor profile of the coffee to the base spirit, which is often grappa.
Coffee liqueurs add roundness and a roasted depth to cocktails, but they overpower other flavors quickly.