Basic Information on Kosher

Milk products and meat products may not be eaten together in the same meal, much less cooked together. Jewish law thus mandates a set of 'fence' laws that prevent this from happening; cooking meat and milk together is prohibited, even if it is not eaten, eating milk and meat together is prohibited even if they are not cooked together, and no benefit can be attained from such activity; for instance, one cannot even serve meat and milk together to an animal.

Note that in most current forms of Judaism (but not among all Karaites, Ethiopian Jews and some Persian Jewish communities), this even applies to the flesh of birds, not just mammals. Most observant Jewish homes maintain two sets of silverware, cookware, cups, and dishes. One is for milk (Yiddish milchig, Hebrew halavi) dishes, and one is for meat (Yiddish fleishig or fleishedik, Hebrew basari) dishes. This prevents any trace of meat or dairy from being accidentally mixed. (Foods that contain neither milk nor meat are considered "neutral" -- Yiddish pareve, modern Hebrew parve).