Restrictions on the foods suitable for Jews are derived from rules in the books of Leviticus and Deuteronomy. Animals must be slaughtered and prepared in the prescribed way, in which the blood is drained from the body, while certain creatures, notably pigs and shellfish, are forbidden altogether. Meat and milk must not be cooked or consumed together, and separate utensils must be kept for each. Strict observance of these rules is today confined mainly to Orthodox Jews
mid 19th century: from Hebrew kāšēr 'proper'