everlasting darkness; eternal night
A literary and somewhat archaic term for a state of perpetual darkness, often used in mythological or poetic contexts.
神話では、世界はかつて常闇に包まれていた。
In mythology, the world was once shrouded in everlasting darkness.
The exact derivation is uncertain; the kanji 常 (everlasting) and 闇 (darkness) directly convey the meaning.