The Hebrew noun aphelah (from root aphal) denotes thick darkness, deep gloom, or dense obscurity. It is a stronger word than ordinary darkness (choshek), conveying the sense of impenetrable blackness — the kind associated with judgment, the absence of God's light, or supernatural terror.
Scripture uses aphelah to describe both physical darkness (the darkness of Egypt's plague) and spiritual/moral darkness (the path of the wicked, the darkness of sheol). Theologically, darkness in Hebrew thought is the antithesis of God's presence and glory. The contrast between God as light and the darkness of sin and judgment runs through the entire biblical narrative. Aphelah heightens this contrast — this is not a minor dimness but a complete absence of divine light.