Beliyaal is a compound word: beli (without) + yaal (profit, worth). Together it means "without worth" or "one who yields nothing." In the OT it describes morally worthless persons — rebels, scoundrels, and those given to evil. By the intertestamental period it became a proper name for Satan himself: Belial, lord of chaos.
The term appears 27 times in the OT, always describing thorough moral corruption. "Sons of Belial" (KJV) are the worst of the worst — those who have no use for God or decency. The NT picks up this usage in 2 Corinthians 6:15: "What harmony is there between Christ and Belial?" — setting God's kingdom in absolute contrast to the realm of worthlessness. Where God gives value and meaning, Belial represents the opposite: empty, fruitless, destructive living.