In biblical times there was a peculiar apparatus that the Israelite High Priest wore. It consisted of a robe to which was attached to an apron-like garment called an ephod. Fastened on the ephod was a breast-piece, which contained twelve precious and semiprecious stones in front and two more at the shoulders, abnay zeekawrone in Hebrew. In a pocket of the breast-piece were two items called the urim and thummim.
There are many ideas about the purpose and function of the ephod’s urim and thummim, but the Bible says little. The urimare mentioned a grand total of four times in the Five Books of Moses and only three more times elsewhere. (I distinguish between the Five Books and the others because there is no evidence that the ephod operated after King David‘s reign.) The thummim are found three times in the Five Books, twice elsewhere.