Kosher is a Hebrew word meaning “fit.” The Torah lays down guidelines for what’s fit, kosher, for a Jew to eat—and what’s not. Here are the general rules:
Kosher meat must come from cud-chewing mammals with hooves that are split, and must be slaughtered and processed in a specific, ‘kosher’ way. Poultry are limited to chickens, ducks and certain other non-predatory birds, which must be prepared and Kosherized similar to kosher beef. The consumer can know if meat/poultry is kosher by looking for a Kosher certification on the packaging.
Kosher fish must have fins and scales. Grains, beans, and legumes (without additional ingredients) are fine. Wines, beverages and anything liquid are accepted as Kosher when bearing a reliable kosher symbol on their label.
Pareve foods are neither meat nor dairy. This means that they contain no meat or dairy derivatives, and have not been cooked or mixed with any meat or dairy foods.
Fresh fruits and vegetables are never a problem unless they have bugs. See infestation.