The noun skotos denotes darkness — both the physical absence of light and, far more prominently in the NT, the spiritual state of those who are separated from God: moral darkness, ignorance, and the domain of evil. It stands in absolute contrast to phōs (G5457, light), and this light/darkness dualism is one of the NT's most pervasive theological frameworks.
Isaiah 9:2 / Matthew 4:16 establishes the Messianic program: 'The people living in darkness [skotos] have seen a great light.' Jesus enters human history as the invasion of divine light into satanic darkness. John 3:19–21 diagnoses the human condition: people loved darkness rather than light because their deeds were evil. Skotos is not just ignorance but willful preference for a darkened moral state. Colossians 1:13 is the gospel in miniature: God 'has rescued us from the dominion of darkness [skotos] and brought us into the kingdom of the Son he loves.' 1 Thessalonians 5:5 applies this redemptive transformation to identity: 'You are all children of light and children of the day. We do not belong to the night or to the darkness [skotos].' Ephesians 5:8,11 draws the ethical consequence: 'You were once darkness [skotos], but now you are light in the Lord. Live as children of light… and have nothing to do with the fruitless deeds of darkness [skotos].'