Ten spiritual realms
The ten spiritual realms are part of Buddhist cosmology and consist of four higher realms and six lower realms. Some schools of Buddhism see them as being external, ten different planes of existence beings can be born into, whilst others see them as states of mind that can be shifted between due to external and internal influences. The following is a description of the ten realms as mental states.
Six realms of desire
The six lower realms are Hell, Hunger, Animality, Arrogance, Humanity and Rapture. These six lower worlds arise automatically from within people’s lives in response to external surroundings. Three of the four remaining worlds are: Learning, Realization and Bodhisattva. These worlds are developed through seeking, discovering and aspiring. The tenth world, Buddhahood, is a condition of pure, indestructible knowledge.
Hell is a condition of total claustrophobic aggression, in which one perceives no freedom of action and has very little life-force (physical or mental energy). One feels totally trapped by one's circumstances, the being is dominated by anger, hatred and frustrated rage and, in extreme cases, the urge to destroy oneself and everything else. It is a very difficult realm to escape from, since the condition tends to be self-perpetuating, with intense suffering and aggression feeding each other (one's sojourn in Hell is described as being measured in kalpas). Paradoxically, although this state is characterized by claustrophobia, there is an obsession with filling up any space which may present itself, since the space itself is perceived as being threatening. The desire not to fall into this condition is a powerful incentive for people to make efforts to rise above this state in daily life.
Hunger is a condition characterized by possessiveness and insatiable desires which govern one's actions, for food, power, wealth, fame, pleasure and so on. In this state one is tormented by relentless craving and the inability, even when the desire is achieved, to enjoy its fruition. This realm is characterized by a total lack of willpower and the disregard of all things except the fulfillment of desires.
Animality is a condition in which one is governed by instinct, in which one has no sense of morality and lives only for the present moment. In this state one won't hesitate to prey on weaker beings for personal gain, and will try to attract the attentions of stronger beings in order to side with them. This realm is characterized by the total lack of good judgment and reason.
Arrogance is the condition in which one is dominated by the selfish ego, competitiveness, paranoid jealousy and the need to be superior in all things, being them mundane or spiritual. Though potentially virtuous, the experiencer is a slave to his/her delusions, considering ones ego and beliefs as more important than - and superior to - others. This realm is characterized by viewing other beings as potential threats. Still, the rest of the experience in this realm is generally quite pleasant as compared to the human realm.
Humanity (or passionate idealism)
Humanity is the state in which the discriminating awareness and the thinking mind are most highly developed. It is characterized by ambitious passion for abstract ideals and role models, and is unique among the lower realms in providing both the potential means and the motivation to transcend suffering. It is also characterized by shortness of life, in comparison to the Deva and Asura realms, and by being extremely rare in occurrence, without refuge in the Dharma.
Heaven is the condition of pleasure, when one's desires are fulfilled and one experiences short-lived but intense feelings of joy. Unlike the true happiness of Buddhahood, however, this state is temporary and, like Humanity, easily disrupted by even a slight change of circumstances. One will inevitably descend to a lower realm once the joy dies away. This realm is characterized by not feeling negative emotions and being less vulnerable to external influences than the lower realms.
The majority of sentient beings spend most of their time moving between these six conditions of life, from Hell to Rapture, governed by their reactions to external influences and therefore highly vulnerable to all of the six lower realms, the experiencer's emotional state is totally controlled by externals. Indeed his/her entire identity is based on externals.
Learning is a condition in which one seeks some skill, lasting truth or self-improvement through the teachings of others. To access this realm, the experiencer must first develop the desire to gain wisdom and insight into the true nature of all things, free from delusion. This realm is characterized by the seeking of truth and wisdom through external sources, e.g. other people and pre-recorded information (usually texts).
Realization (or absorption)
Realization is a state in which one discovers a partial truth through one's own observations, efforts and concentration. Usually to access this realm the experiencer must first have decided external sources are inferior to internal sources, e.g. his/her own mind. This realm is characterized by the seeking of truth and wisdom through direct internal perception.
The two above realms are collectively known as 'the two vehicles'. Even though these realms are based upon the desire to increase wisdom and insight, ego is still present, as these desires are primarily self-oriented.
Bodhisattvahood is a condition in which one not only aspires for personal enlightenment but also devotes oneself to relieving the sufferings of others through compassionate and truly altruistic actions, e.g. helping others. This realm is characterized by the feeling that happiness achieved through the benefit of others is superior to happiness achieved through the benefit of only the self.
Buddhahood is the highest of the Ten Worlds, a condition of pure, indestructible happiness which is not dependent on one's circumstances. The experiencer is totally free from all delusion, suffering and anger. It is a condition of perfect and absolute freedom, characterized by boundless wisdom, courage, compassion and life force. This realm is difficult to describe and is generally only obtained through the direct internal perception of the realm of realization. This realm is characterized by not being shifted into lower realms due to external sources, and the non-reliance on external sources for happiness. This realm is manifested outwardly through the actions of the realm of bodhisattvahood.
Interpenetration of the Ten Realms
Each of the Ten Worlds possesses all Ten Worlds. Each has the potential to reveal any of the others at any moment. Some sects of Buddhism believe that as people practice Buddhism they make Buddhahood the dominant state of their lives, as it acts as a kind of filter, revealing the positive aspects of the other nine worlds from Hell to Bodhisattva.
The realms are labelled the same by Buddhist sects that see them as planes of existence, the difference being the only way to shift between them is through rebirth. This is governed by karma (action and volition: the choices made during life).
These two interpretations can also be conceived of as coexisting.