Kosher is a word that comes from a Hebrew root meaning fitting or proper. In Judaism it refers to the following of dietary laws. In modern parlance, it has taken on new meaning which reflects its root.
Kosher
In Judaism – Conforming to dietary laws; ritually pure: kosher meat.
Selling or serving food prepared in accordance with dietary laws: a kosher restaurant.
In slang – Legitimate; permissible
Genuine; authentic