Apple cider is an unfiltered, unsweetened, non-alcoholic beverage made from apples, usually from specializing cider apples. Apple cider is easy and inexpensive to produce. It may be opaque due to fine apple particles in suspension and may be tangier than conventional filtered apple juice, depending on the apples used (Wikipedia, nd).
An allergic reaction to apple cider is probable if you also have an apple allergy. Although most apple cider brands only contain apples, other seasonal releases may include spices as well. Visit your allergist if you have an allergic reaction.
Apple cider is primarily found as a drink, but can also be used in a wide variety of recipes. Such items include apple cider doughnuts, candy, and spiced cider.