Ojo is a methodology for becoming a Buddha, as defined by the Mahayana Buddhism.
Because the real Shakyamuni seson (World-Honored One; honorific name for Gautama Buddha) no longer existed, the idea of Birth in the Pure Land was conceived to seek assurance in the attainment of Buddhahood by receiving the guidance of Buddha. There are various interpretations of pure lands for rebirth, but it generally means the Buddhist paradise that is considered to be the pure land of Amida Buddha. This is referred to as gokuraku ojo (peaceful death). whereby 'o' means to go to the Pure Land (of Amida Buddha), 'jo' means to kesho (be reborn) in that land and to be reincarnated in the Pure Land is referred to as Renge kesho.
Kesho is one of the four categories of birth for creatures; the others are taisho ransho, shissho and kesho.
Taisho: To come out of the mother's body, as with humans and animals.
Ransho: To be hatched from eggs, as with birds
Shissho: To come out of a moist environment, as with insects
Kesho: To come into existence in a converted form as a consequence of one's past actions
Such as celestial beings
It is said that to be born in the Pure Land of Amitabha means to be reincarnated as the result of the karma that is generated in that land. Renge kesho means to be reincarnated surrounded by lotus (renge) flowers in the Pure Land of Amitabha.
The original meaning of ojo is to go to the country of Buddha (India), be born in that land to become a Buddha, and to attain enlightenment. Thus the primary meaning of ojo is to become a Buddha but not simply to go to the Pure Land of Amitabha.
In the context of Mahayana Buddhism, it was considered that because one must have juki (endorsement) by Buddhas to attain Buddhahood based on their guidance, the way to become a Buddha is to be born in Buddha lands. It was further considered that, given independent self-training without Buddhas' guidance nor their juki (endorsement), one could become an Arakan or Byakushibutsu; however, once they become either Arakan or Byakushibutsu they could not attain Buddhahood.
In Buddhism, to attain enlightenment is to attain the state of perfect self-effacement. For one to understand that he is empty and nothing, the state of 'ego' should not exist while one is in training. Assuming that it is impossible to attain Buddhahood as long as there is ego-consciousness, it will be impossible to remove the ego-consciousness by oneself. It is the standpoint of Jodo-mon (Gateway of the Pure Land) that this is the reason one needs to meet and see Buddha to attain Buddhahood.
The general meaning of 'ojo'
Because when people die they are immediately reborn in the land of Buddha, ojo, as in 'gokuraku ojo' (go to paradise) and 'jodo ojo' (go to the Pure Land) generally means birth after death. Additionally, the world one goes to when he or she dies is the world of Buddha, so to be born in that world is to become a Buddha.
Given the foregoing, it is considered that ojo means to become a Buddha. In reality, because ojo means to die and, moreover, to become a Buddha, it is considered that the line of thought where one would become a Buddha upon death became common. Death due to a natural cause, such as succumbing to old age and particularly multiple organ failure due to old age, is often referred to as a peaceful death.
It is considered that this definition of 'ojo' became further secularized, so that it meant 'to be cornered and not know what to do.'