Maitreya is regarded as a future Buddha of this world in Buddhist eschatology. Between Gautama Buddha and Maitreya Buddha, there is no Buddha in between, and this period, based on human calendar, is roughly five hundreds seventy six millions years.
According to Buddhist tradition, Maitreya is a Bodhisattva who will appear on Earth in the future, achieve complete enlightenment, and teach the pure dharma. According to Sutras, Maitreya will be a successor to the present Buddha, Gautama Buddha (also known as Sakyamuni Buddha). The prophecy of the arrival of Maitreya refers to a time in the future when the dharma will have been forgotten by most of the terrestrial worlds. This prophecy is found in the canonical literature of all major schools of Buddhism.
The name Maitreya is derived from the Sanskrit word maitri "loving-kindness", which is in turn derived from the noun mitra "friend".
Maitreya currently resides in the Tusita Heaven, said to be reachable through meditation. Gautama Buddha also lived here before he was born into the world. Although all Bodhisattvas are destined to become Buddhas, the concept of a Bodhisattva differs greatly in Theravada and Mahayana Buddhism. In Theravada Buddhism, a Bodhisattva is one who is striving for full enlightenment, whereas in Mahayana Buddhism, a Bodhisattva is one who has already reached a very advanced state of grace or enlightenment but holds back from entering into Nirvana so that he may help others.
Once Maitreya becomes a buddha, he will rule over the Ketumati Pure Land.
Maitreya's arising would be no different from the arising of Gautama Buddha, as he achieved full enlightenment as a human being and died, entering Parinibbana (般涅槃).
Kalpa(劫) is a Sanskrit word meaning an aeon, a relatively long period of time in Hindu and Buddhist cosmology. There are four different lengths of kalpas. A regular kalpa is approximately 16 million years long (16,798,000 years), and a small kalpa(小劫) is 1000 regular kalpas, or about 16 billion years. Further, a medium kalpa(中劫) is roughly 320 billion years, the equivalent of 20 small kalpas. A great kalpa(大劫) is 4 medium kalpas, or around 1.28 trillion years.
According to Buddhist tradition, each great kalpa has 1,000 Buddhas. The previous kalpa was the vyuhakalpa (Glorious aeon)(過去莊嚴劫), the present kalpa is called the bhadrakalpa (Auspicious aeon)(現在賢劫), and the next kalpa will be the naksatrakalpa (Constellation aeon)(星宿劫).
Vipassī (毘婆尸佛) (the 998th Buddha of the vyuhakalpa)
Sikhī (尸棄佛) (the 999th Buddha of the vyuhakalpa)
Vessabhū (毗舍浮佛) (the 1000th and final Buddha of the vyuhakalpa)
Kakusandha (拘留孫佛) (the first Buddha of the bhadrakalpa)
Koṇāgamana (拘那含牟尼佛) (the second Buddha of the bhadrakalpa)
Kassapa (迦葉佛) (the third Buddha of the bhadrakalpa)
Gautama (釋迦牟尼佛) (the fourth and present Buddha of the bhadrakalpa)
Maitreya will be the fifth Buddha of the bhadrakalpa, and his arrival will occur after the teachings of Gautama Buddha are no longer practiced.
The scriptures say that Maitreya will attain bodhi (菩提) in seven days (which is the minimum period), by virtue of his many lives of preparation for Buddhahood similar to those reported in the Jataka tales.
Budai (布袋) was an eccentric Chan (禪) monk, and his name means "Cloth Sack". The name comes from the bag that he is conventionally depicted as carrying. He is usually identified with or seen as an incarnation of Maitreya, the future Buddha. He is almost always shown smiling or laughing; hence his nickname is the Laughing Buddha.