Root beer extract is (now) used as flavoring to make a soft drink called Root Beer which dates back to the 1800's. The original flavoring for the beverage was sassafras. The main flavoring used today is wintergreen or even sassafras extract.
Besides beverages this extract can be it can be used in anything from BBQ sauce, cookie recipes, cakes, ice cream and even fudge and cheesecake.
Watkins root beer extract
Propylene glycol, water, natural and artificial flavor.
McCormick Root Beer Concentrate:
Caramel color, water, corn syrup, wild cherry bark extractives and other natural extractives, natural and artificial flavors, methyl salicylate (flavoring agent), vanillin, gum arabic, gum tragacanth, and sulfiting agents.