Food is kosher when it conforms to Jewish dietary laws as outlined in the Bible books Leviticus and Deuteronomy. The books specify particular foods as well as kosher rules for food preparation and consumption.
For example, eating meat from animals with cloven hooves, such as pigs, is not kosher. Shellfish are not kosher because the Jewish law states that only fish with fins and scales are kosher. The Jewish law also requires that animals must be slaughtered in a certain way. Dishes are not kosher if non-kosher ingredients or utensils are used in their preparation. Some foods may not be eaten together, such as milk and meat. Kosher certifying agencies exist to authenticate prepackaged foods, which are then labeled as kosher.