Kosher food is food that has been made with out certain ingredients in a manner that has been approved by a Rabbi... Animals must be killed in a certain way as well... here is some info on it http://en.wikipedia.org/wiki/Kosher_foods

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. [...] Food that is not kosher is commonly referred to as treif (lit. torn, from the commandment not to eat animals that have been torn by other animals). [...] General Rules Although the details of kashrut are extensive, the laws all derive from a few fairly simple, straightforward rules: 1. Certain animals may not be eaten at all. This restriction includes the flesh, organs, eggs and milk of the forbidden animals. 2. Of the animals that may be eaten, the birds and mammals must be killed in accordance with Jewish law. 3. All blood must be drained from the meat or broiled out of it before it is eaten. 4. Certain parts of permitted animals may not be eaten. 5. Fruits and vegetables are permitted, but must be inspected for bugs 6. Meat (the flesh of birds and mammals) cannot be eaten with dairy. Fish, eggs, fruits, vegetables and grains can be eaten with either meat or dairy. (According to some views, fish may not be eaten with meat). 7. Utensils that have come into contact with meat may not be used with dairy, and vice versa. Utensils that have come into contact with non-kosher food may not be used with kosher food. This applies only where the contact occurred while the food was hot. 8. Grape products made by non-Jews may not be eaten. 9. There are a few other rules that are not universal. - http://www.jewfaq.org/kashrut.htm (Follow the link for more detail.)