The Hebrew word Urim (אוּרִים) is the plural of ur (light/fire) and refers to one component of the Urim and Thummim — the sacred priestly oracle carried in the breastpiece of the high priest. The precise nature of these objects is unknown; they served as a means by which God communicated His will to Israel's leaders.
The Urim and Thummim (Lights and Perfections) represent God's provision for seeking divine guidance in times of uncertainty. They appear at key moments of national decision: before battles, in selecting leaders, in determining God's will when prophecy was absent. Their presence in the high priest's breastpiece — worn "over his heart" — symbolized that Israel's leader carried the means of divine communication close to his heart. The Urim is associated with the tribe of Levi (Deuteronomy 33:8). After the exile, Israel lacked the Urim and Thummim and awaited a priest with them again (Ezra 2:63) — a longing fulfilled in Christ, our Great High Priest who perfectly mediates God's will.