What is Kosher?

Kashrut or kashruth, kashrus (Hebrew: כַּשְרוּת, kašrûṯ) or "keeping kosher" (Hebrew: כָּשֵר, kāšēr) is the name of the 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). The equivalent for Muslims, as per Islam, is Halal food.

Food not in accord with Jewish law is termed treif, trafe (Yiddish: טרייף from טְרֵפָה ṭərēp̄āh, "torn"); the Hebrew term refers to animals (from a kosher species such as cattle or sheep) which had been either incorrectly slaughtered or mortally wounded by wild beasts and therefore were not fit for human consumption. Among Sephardim, it typically only refers to meat that is not kosher. Sometimes, non-kosher food in general may be dismissed with the colloquial term chazir-treif, which literally means "as unfit as pork", the pig having become perhaps the most notable symbol of the non-kosher animal.

Many of the basic laws of kashrut are in the Torah's Book of Leviticus, with their details set down in the oral law (the Mishnah and the Talmud) and codified by the Shulchan Aruch and later rabbinical authorities. Many varied reasons have been offered for these laws, ranging from philosophical and ritualistic, to practical and hygienic; see below for examples and explanations.

The word kosher has been borrowed by many languages, including English. In its strictest meaning it means "fit", but as in Yiddish it also generally means legitimate, acceptable, permissible, genuine or authentic in a broader sense.