Jikkai (the Ten Realms) (十界)
Jikkai means all the states of a human spirit categorized into 10 types according to the creed of the Tendai sect, including Rokudo (six posthumous worlds) as well as the four of states of Shomon, Enkaku, Bosatsu and Buddhahood. It is also referred to as jikkairon, jippokai (十方界) or jippokai (十法界). It is written in the 50th volume of the "Bussotoki" (Record of the Lineage of the Buddha and the Patriarchs), showing the tradition of Tendai thought.
There are the worlds of hell, hungry spirits, animals, Asura, humans and heaven, as well as the worlds of voice-hearers, cause-awakened ones, Bosatsu and the spiritual realm of Buddhahood, all of which are collectively called Jikkai.
Rokudo
Rokudo indicates the (reincarnated) worlds repeated mainly within a human.
The world of hell
This is a state of suffering from every fear. Refer to Hell (Buddhism).
The world of hungry spirits
A state of being a hungry spirit that sticks with something in front.
The world of animals
A state of acting based on an animal instinct. It refers to a state in which one acts based on desires such as appetite, a desire for sleep, sexuality, cupidity, the lust to dominate and so forth.
The world of Asura (fighting demon)
A state of trying to solve a problem using 'military force' without conversation. It encompasses everything from a general quarrel to a war between nations.
The world of humans
This is a calm state. However, it may also refer to a humanly suspicious mind.
The world of heaven
A state of feeling various 'delights.'
It generally refers to an instantaneous delight.
Furthermore, three of the cursed parts of human existence, including the worlds of hell, hungry spirits and animals, are sometimes categorized as San-akushu (three evil worlds of hell) (also referred to as San-akudo).
The world of Asura is sometimes added to San-akushu and is therefore called Shi-akushu (four evil worlds of hell).
Contrary to San-akudo, the three worlds of Asura, human and heaven can be collectively called San-zendo.
Contrary to Shisho (described later), being called Gokai, Rokudo is also referred to as Meikai.
Shisho
Shisho means the four worlds added to Rokudo in the Tendai sect. These worlds are spiritual states of human existence instead of allegorical worlds. Shisho is also referred to as Gokai.
The worlds of voice-hearers
This is the state of learning Buddhism. It encompasses the state of 'learning' not only Buddhism but also philosophy, literature, physics, and even mass entertainment and children's nonsense.
The world of cause-awakened ones
A state of having achieved self-conscious enlightenment internally by being associated with Buddhism. It is fundamentally different from the 'enlightenment' of Buddhahood.
The world of Bosatsu
This is the state of acting as an envoy of Buddha. It refers to the 'action' itself, regardless of one's intention.
The spiritual realm of Buddhahood
A state of enlightenment.