Orange liqueurs are used a great deal in making cocktails, and in desserts.
The category includes liqueurs made from mandarin oranges (or “tangerines“), which technically aren’t exactly the same thing as oranges.
They are made from the skins of oranges, either by chopping the skins up and letting them soak in the alcohol, then straining them out, or by creating an essence of the orange skin oil and then adding that to the alcohol. Usually skins of bitter oranges are used, but some such as Cointreau also add some skins from sweet oranges.
Some orange liqueurs are very sweet, some are drier. Different brands have different proof strengths.
See also: Grand Marnier Day
Substitutes
Frozen orange juice concentrate; orange juice which you have simmered to evaporate some of the water away to concentrate the flavour.