The words in the head of a Golem, determining its task and function. The Hebrew word "chem" (שם, correctly transcribed as "shem") means "name". The chem usually consists of a slip of paper, on which a priest has written a suitable phrase, maybe a commandment, from a holy text of the religion of the priest's choosing. For some golems, work instructions are written instead of holy text. Some of the more ancient golems, such as Anghammarad, had clay tablets in their head instead of paper.
Some golems are set free by placing their receipt, stating that the holder of the receipt is the owner of the golem, in their head with the chem. The golem Dorfl recieved his receipt, thereby becoming his own owner and the first free golem.
The wily Havelock Vetinari has taken advantage of this by re-writing the chem to turn free Golems into dedicated Government agents, such as Mr Pump, who tracks down and arrests Moist von Lipwig in accordance with the new words in his head, put there by Vetinari...
In many Roundworld tales, the golem is inscribed with magic or religious words that keep it animated. Writing one of the names of God on its forehead, a slip of paper in its mouth, or inscribed on its body, or writing the word Emet (אמת, "truth" in the Hebrew language) on its forehead are examples of such words. By erasing the first letter aleph in Emet to form Met (מת, "dead" in Hebrew) the golem could be deactivated. Another way is by writing a specific incantation in the owner's blood on calfskin parchment, and placing it in the mouth. (Which, of course, Dorfl does, in a desperate attempt to revive Father Tubelcek after he has been attacked by the Golem King, in Feet of Clay). Removing the parchment will deactivate the golem. It is likely that this is the same incantation that the Rabbi recites in the classic narrative. Though it was said that taking the golems chem would "kill" them Dorfl regained himself in order to "kill" Meshugah claiming that "words in the heart can not be taken".