Kashrut
Among the numerous laws that form "kashrut" are prohibitions on the consumption of certain animals (such as pork and shellfish), mixtures of meat and milk, and the commandment to slaughter mammals and birds according to a process known as "shechita". There are also laws regarding agricultural produce that might impact the suitability of food for consumption.
Jewish cuisine
Gefilte fish (from German "gefüllte" "stuffed" fish) was traditionally made by skinning the fish steaks, usually German carp, de-boning the flesh, mincing it and mixing with finely chopped browned onions (3:1), eggs, salt, pepper, and vegetable oil. The fish skin and head were then stuffed with the mixture and poached. The religious reason for a boneless fish dish for the Sabbath is the prohibition of separating bones from food while eating [the prohibition of 'borer', separating]
A more common commercially packaged product found today is the "Polish" gefilte fish patties or balls, similar to quenelles, where sugar is added to the broth, resulting in a slightly sweet taste. Strictly speaking they are the fish filling, rather than the complete filled fish. This method of serving evolved from the tradition of removing the stuffing from the skin, rather than portioning the entire fish into slices before serving.