In Judaism, foods are divided into two groups—kosher, which is allowed, and treif, which is forbidden.
According to the Tora, only animals which chew and have cloven hooves are permitted for eating, and four animals are expressly forbidden as food—the hare, camel, hyrax, and pig. Also forbidden are insects and reptiles.
In addition to this, even kosher animals must be slaughtered using a specific process for the meat to be considered acceptable for use by the Jewish people. Because the Torah prohibits the consumption of blood, all blood must be removed from the meat through soaking, salting, or broiling before consumption. Because of the difficulty in completely removing blood from it, the liver is not eaten.
Meat and dairy products may not be eaten together, and must be kept separate. Interestingly, utensils, plates, bowls, and even sinks and dishwashers can inherit a “meat” or “dairy” status through prolonged contact with either type of food. For example, if a bowl was used to contain milk, and then that bowl was placed in the dishwasher, that dishwasher rack would inherit the “milk” status. It could not, then, be used to clean a dish that had been exposed to meat. The two, and anything that touches them, must always be kept separate under Jewish law.
All plant-based foods are kosher except for wine and other grape products produced by non-Jews.
As you can see, Jewish dietary laws are somewhat complex—keep this in mind if you find yourself serving a Jewish friend!