Gelatin may contain pork. Pork and beef are both common ingredients in gelatin. In order to determine which has been used, the ingredient list should be consulted.
Gelatin, particularly kosher gelatin, is usually made with fish, since pork is forbidden in the kosher diet. Vegan gelatin is made from seaweed, since no meat or animal products of any kind are eaten in the vegan lifestyle.
Gelatin is used for multiple purposes. Aside from foods, it is an agent commonly found in health and beauty products. Gelatin is also the primary component of the outside of pill capsules and is what makes them dissolve when they are penetrated by moisture.