The word kosher (כשר, Kasher) refers to food and bevarages that are in accordance with kashrut (כשרות), the set of Jewish dietary laws. Kosher, in a broader sense, refers to anything that is ritually eligible, in accordance with the rules and that is right, proper and acceptable. This word became a colloquialism in many languages, including Czech and English. In Czech, there is an obsolete word kosher, which was the name for a Jewish butcher, who is commonly known as a shochet. It is necessary to realize that meals that come from Jewish cuisine are not kosher, unless they are prepared in accordance with Jewish dietary laws.
The Torah describes what is kosher in its Books of Wayiqra (Leviticus) and Devarim (Deuteronomy). There is no rational explanation of kashrut (chukim), which means that the reason is the need to 'listen to G-d and emulate His holiness.' There are two frequently mentioned supporting arguments which, however, are not the explanation of kashrut. These include health reasons and educational reasons. While the first one says that kashrut is a prevention of disease and parasites, the latter one says that kashrut is a constant reminder of Judaism and Jewish education for children.
The Torah lists the permitted and forbidden animals. In regard to mammals, the Torah permits to eat cloven-footed and rumirant animals. These include cattle, goats, sheep, big game (e.g. deers, bisons etc.). Forbidden mammals include pigs, rabbits, hares, horses etc. In regards to birds, the Torah explicitly forbids some species, like bird of prey and scavengers. Permitted birds include poultry (chickens, ducks, geese, turkey, quails, pheasants and pigeons). Milk and eggs can be consumed only from animals that are kosher themselves. It is possible to eat any fish that has fins and scales (the scales must be ctenoid or cycloid). Carnivorous fishes, eels, sharks, stingrays, sturgeons (including caviar) and seafood are forbidden. It is also forbidden to eat reptiles, amphibians and insects (excluding some locusts). It is expressly forbidden to eat dead animals and carrions (nevela) and sick and torn animals (treyf).
One of the principles of kashrut is a strict prohibition of mixing meat food (besar) and dairy food (chalav), which is based on the verse 'Thou shalt not boil a kid in his mother's milk.' This means that it is forbidden both to cook such food together and eat it as well. Religious families separate dishes and utensils for a meat and dairy food. It is also forbidden to benefit from a sale of such mixed food. There is a specific period that one has to wait between eating dairy and eating meat and vice versa. These periods vary throughout Jewish communities. One waits shorter period when eats dairy at first and then meat (not for hard cheeses). It is usually about half an hour or one can eats a parve (Parve is a dish that is neither meat nor dairy. This include fruits, vegetables, grains, eggs, fishes, pasta, etc.) and rinse his/her mouth. In reverse order, i.e. when one eats first meat and then dairy, he/she has to wait from one to six hours, according to particular Jewish community.
A consumption of blood is strictly forbidden. This prohibition is based on the verse 'Whosoever eateth it [blood] shall be cut off', which is explained by another verse 'the life of all flesh is the blood thereof.' Animals undergo shechita (a special method of slaughter), which drains blood out of their body. The remaining blood is removed by melicha. This prohibition does not apply to fishes.
Jewish community in Prague publishes an annual guide of kosher food, which sets out a list of appropriate shops, products, food, beverages, and forbidden non-kosher additives.