What is kosher?!
Answers: what makes food kosher?
Kosher refers to Jewish dietary laws. A lot of it has to do with what kind of meats are acceptable to eat, whether it be a particular kind of animal or how the animal is slaughtered. There are also rules around kinds of foods that can be mixed. For instance, meat and cheese cannot be mixed, meaning you can't eat meat and dairy products together at the same meal, or even use a utensil on one and then use it on another.
There are also some foods under Jewish dietary laws that must be prepared by Jews, such as wine and cheese. For more details, Wikipedia does a decent job of breaking down exactly what is kosher and what is not.
sautled in vinegar.
Kosher commonly refer to as Kashrut.
Kashrut (also kashruth or kashrus) refers to Jewish dietary laws. Food in accord with halakha (Jewish law) is termed kosher in English, from the Hebrew term kashér, meaning "fit" (in this context, fit for consumption by Jews according to traditional Jewish law). Jews may not consume non-kosher food (but there are no restrictions for non-dietary use, for example, injection of insulin of porcine origin).
Food that is not in accord with Jewish law is informally called treif.
In the technical sense, treif means "torn" and refers to improperly slaughtered meat. Meat from a non-kosher animal is called a neveila which literally means "an unclean thing".
Many of the basic laws of kashrut are derived from the Torah's Books of Leviticus and Deuteronomy, with their details set down in the oral law (the Mishnah and the Talmud) and codified by the Shulchan Aruch and later rabbinical authorities. The Torah does not explicitly state the reason for most kashrut laws, and many varied reasons have been offered for these laws, ranging from philosophical and ritualistic, to practical and hygienic.
By extension, the word kosher means legitimate, acceptable, permissible, genuine or authentic, in a broader sense.
The laws of kashrut derive from various passages in the Torah, and are numerous and complex.
Foods are kosher when they meet all criteria that Jewish law applies to food and drinks. Invalidating characteristics may range from the presence of a mixture of meat and milk, to the use of produce from Israel that has not been tithed properly, or even the use of cooking utensils which had previously been used for non-kosher food.
Islam has a related but different system, named halal, and both systems have a comparable system of ritual slaughter
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http://www.jewfaq.org/kashrut.htm
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