Kosher means suitable for use or consumption in accordance with applicable laws of Judaism. It is a Hebrew word, and when used informally kosher can also mean proper, authentic or genuine.
The Jewish laws regarding whether or not something is kosher date back more than 3,000 years. These laws have their basis in both the written and the oral Torah. In order to meet kosher requirements regarding meat, individuals may only eat mammals that have cloven hooves and chew their cud and seafood that has fins and scales. Thus, pigs and shellfish are not kosher, while cows, tuna and salmon are kosher.