The Ephod and the Breastpiece of Judgment

The ephod appears to have been a kind of fancy, sleeveless garment that the high priest would wear over his torso. The breastpiece, hoshen was about nine inches square and had mounted on it 12 gems in four rows with each gem engraved, like a seal, with the name of an israelite tribe. So because the breastpiece contained the urim and thumim, and because you could use these to get judgments from god about what you should do, that's why they called it the breastpiece of judgment.