The wheel of samsara divided into six domains of rebirth.
The Six Realms turn the wheel of rebirth into six destinations — gods, jealous demigods, humans, animals, hungry ghosts, and hell-beings — each a world your karma sends you to, none of them permanent. Read literally they are places; read inwardly they are states of mind: pride, envy, craving, ignorance, all conditions one can inhabit now.
The Six Realms unlock a psychology disguised as a cosmology, mapping suffering's varieties as worlds and tying every experience to cause and consequence. Crucially, all six lie within samsara — even heaven is a trap — reframing the goal not as ascent but as exit.