Six Realms of Existence in Zen Buddhism.

A quote.

'Six Realms of Existence:

In ascending scale these are the six realms of:
- hell,
- pretas (or hungry ghosts),
- beasts,
- asuras (or fighting demons),
- human beings,
- devas (or heavenly beings),

All creatures in these realms are tied to the ceaseless round of birth-and-death, that is, to the law of causation, according to which existence on any one of these planes is determined by antecedent actions.

In Buddhism these planes are depicted as the spokes or segments of the 'wheel of life.' This 'wheel' is set in motion by actions stemming from our basic ignorance of the true nature of existence and by karmic propensities from an incalculable past, and kept revolving by our craving for the pleasures of the senses and by our clinging to them, which leads to an unending cycle of births, deaths, and rebirths to which we remain bound.

The Six Realms are the worlds of the unenlightened.

Buddhism also speaks of four realms of enlightened existence, sometimes called the "four holy states". In ascending order, these are the worlds of:
- sravakas,
- pratyekabuddhas,
- bodhisattvas,
- full buddhas.

A sravaka is one who hears the teaching of the Buddha and accepts it into his heart, thereby attaining enlightenment. Prateyakabuddhas ("private buddhas") are those who carry on solitary practice and reach enlightenment without a teacher.

Finally. at the highest two levels of enlightened existence are Bodhisattvas and full Buddhas.

Unlike those in the lower Six Realms, the enlightened know the joy of inward peace and creative freedom because, having overcome their ignorance and delusion through Knowledge, they are freed from enslavement to karmic propensities arising from past delusive actions, and no longer sow seeds which will bear fruit in the form of new karmic bondage.

Enlightenment, however, does not suspend the law of cause and effect.

When the enlightened man cuts his finger it bleeds, when he eats bad food his stomach aches.

He too cannot escape the consequences of his actions.

The difference is that because he accepts - that is, sees into - his karma he is no longer bound by it, but moves freely within it.

-- Quoted from: 'The Three Pillars of Zen' by Roshi Philip Kapleau.
(I've reformatted the text to be easier to read, and omitted the language translation comments).