“Kosher” is the definition given to foods prepared in accordance with Jewish Law as relating to foodstuffs. The Torah requires that beef cattle and chickens be slaughtered in accordance with these laws, in a ritual called Shechita. Only a trained person called a Shochet may perform the ritual, before which a special prayer called Beracha must be uttered.
The aim of the ritual is to slit the throat of the animal while still alive, and so provoke instantaneous and painless death. The cut must be made with a specially sharpened knife and sever the trachea, the esophagus and the principal veins and arteries of the neck, so provoking massive bleeding. After slaughter, an inspector verifies the internal organs of the animal to spot any signs of physiological abnormality that would render the meat non-Kosher.
These days the entire Kosher process, including salting, is carried out in the meat packer’s establishment under the supervision of a rabbi, who guarantees that the food is Kosher. Products also carry a seal certifying that the entire process for production of the foodstuff was in compliance with the Torah.
Source: AMI Foundation e Orthodox Union.