Kashrut is the body of Jewish law dealing with what foods we can and cannot eat and how those foods must be prepared and eaten. "Kashrut" comes from the Hebrew root Kaf-Shin-Resh, meaning fit, proper or correct. It is the same root as the more commonly known word "kosher," which describes food that meets these standards. The word "kosher" can also be used, and often is used, to describe ritual objects that are made in accordance with Jewish law and are fit for ritual use

Contrary to popular misconception, rabbis or other religious officials do not "bless" food to make it kosher. There are blessings that observant Jews recite over food before eating it, but these blessings have nothing to do with making the food kosher. Food can be kosher without a rabbi or priest ever becoming involved with it: the vegetables from your garden are undoubtedly kosher (as long as they do not have any bugs, which are not kosher!). However, in our modern world of processed foods, it is difficult to know what ingredients are in your food and how they were processed, so it is helpful to have a rabbi examine the food and its processing and assure kosher consumers that the food is kosher. This certification process is discussed below.

There is no such thing as "kosher-style" food. Kosher is not a style of cooking. Chinese food can be kosher if it is prepared in accordance with Jewish law, and there are many fine kosher Chinese restaurants in Philadelphia and New York. Traditional Ashkenazic Jewish foods like knishes, bagels, blintzes, and matzah ball soup can all be non-kosher if not prepared in accordance with Jewish law. When a restaurant calls itself "kosher-style," it usually means that the restaurant serves these traditional Jewish foods, and it almost invariably means that the food is not actually kosher.

Food that is not kosher is commonly referred to as treyf (lit. torn, from the commandment not to eat animals that have been torn by other animals).