'Ad (H5704) is a preposition and conjunction expressing extent of time, space, or degree. It means until, as far as, even to, up to, through, while. Temporally: 'they waited until evening.' Spatially: 'from Dan to Beersheba.' In degree: 'even to death.' It often pairs with min (from) to form the idiom min... 'ad — 'from... to,' expressing comprehensive scope. It appears over 1,200 times in the Hebrew Bible.
The phrase 'ad 'olam — 'forever, unto eternity, even to the age' — is one of the most important theological expressions in the Psalms. God's lovingkindness endures 'ad 'olam (Psalm 136); his throne is established 'ad 'olam. The word 'ad carries the force of unbroken continuity and ultimate destination: God's purposes are not interrupted, they reach their goal.
In the suffering psalms and prophetic passages, 'ad expresses the agonizing question of duration: 'How long, O LORD? Will you forget me forever?' (Psalm 13:1). But the very same word anchors the promise: God's mercy endures 'ad 'olam — until forever, without end.