The word kosher means proper or acceptable, and it has informallyentered the English language with that meaning. The laws of kosher food originate in the Bible, and have been observed by Jews for over 3,300 years. There are three categories of kosher food. The mitzvah of kosher transforms food into a vehicle for holiness, making the kitchen the spiritual hub of the home. "Kashrut" comes from the Hebrew root Kaf-Shin-Reish, meaning fit, proper or correct. 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.
Though Jewish dietary law is very complex, we have given below some general simplified guidelines:-
Certain animals may not be eaten at all. This restriction includes the flesh, organs, eggs and milk of the forbidden animals.
Of the animals that may be eaten, the birds and mammals must be killed in accordance with Jewish law.
All blood must be drained from meat and poultry or broiled out of it before it is eaten.
Certain parts of permitted animals may not be eaten.
Fruits and vegetables are permitted, but must be inspected for bugs (which cannot be eaten)
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).
Utensils (including pots and pans and other cooking surfaces) 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.
Grape products made by non-Jews may not be eaten.
There are a few other rules that are not universal like Bishul Yisroel, Cholov Yisroel, Mevushal.