Kosher as a word, literally meaning “clean” or “pure,” refers to food that has been prepared in accordance with Jewish rules and rituals so it can be eaten by religious Jews.
Kosher food is essentially food that does not have any non-kosher ingredients in accordance with Jewish law. What makes something kosher is that meat and milk products are not mixed together, animal products from non-kosher animals (like pork, shellfish, and others) are not included, and any meat from kosher animals is slaughtered in the correct procedure.
There are a number of other requirements that need to be met, both in the process of food preparation and who performs the process .
Because the "Torah" allows eating only animals that both chew their cud and have cloven hooves, pork is prohibited. So are shellfish, lobsters, oysters, shrimp and clams, because the Old Testament says to eat only fish with fins and scales. Another rule prohibits mixing dairy with meat or poultry.
Jews can ensure they keep kosher by buying products certified as kosher with a mark called a hekhsher that usually identifies the rabbi or group that certified the product.
Not all Jewish people keep kosher, and kosher foods aren't just for Jewish people. For example, some soft drinks are kosher, and people of all backgrounds and religions drink them.
Foods so certified are not "blessed." Rather it means the place they were processed is inspected to make sure kosher standards are maintained. Kosher meat, for example, must be slaughtered without causing pain to the animal, meaning that death occurs almost instantaneously.