The Three Ages of Buddhism are three divisions of time following Buddha's passing: the Former Day of the Law (正法 Cn: zhèngfǎ; Jp: shōbō), the first thousand years (or 500 years); the Middle Day of the Law (像法 Cn: xiàngfǎ; Jp: zōhō), the second thousand years (or 500 years); and the Latter Day of the Law

Mappo

The Latter Day of the Law, is one of the Three Ages of Buddhism. Mappō or Mofa , which is also translated as the Age of Dharma Decline, is the "degenerate" Third Age of Buddhism.- Tradition :...

 (末法 Cn: mòfǎ; Jp: mappō), which is to last for 10,000 years.

The three periods are significant to Mahayana

Mahayana

Mahāyāna is one of the two main existing branches of Buddhism and a term for classification of Buddhist philosophies and practice...

 adherents, particularly those who hold the Lotus Sutra

Lotus Sutra

The Lotus Sūtra is one of the most popular and influential Mahāyāna sūtras, and the basis on which the Tiantai and Nichiren sects of Buddhism were established.-Title:...

 in high regard; e.g., Tiantai

Tiantai

Tiantai is an important school of Buddhism in China, Japan, Korea, and Vietnam. In Japan the school is known as Tendai, and in Korea it is known as Cheontae. Tiantai is also called the "Lotus School", due to its emphasis on the Lotus Sūtra as its doctrinal basis...

 (Tendai

Tendai

is a Japanese school of Mahayana Buddhism, a descendant of the Chinese Tiantai or Lotus Sutra school.Chappell frames the relevance of Tendai for a universal Buddhism:- History :...

) and Nichiren

Nichiren

Nichiren was a Buddhist monk who lived during the Kamakura period in Japan. Nichiren taught devotion to the Lotus Sutra, entitled Myōhō-Renge-Kyō in Japanese, as the exclusive means to attain enlightenment and the chanting of Nam-Myōhō-Renge-Kyō as the essential practice of the teaching...

 Buddhists, who believe that different Buddhist teachings are valid (i.e., able to lead practitioners to enlightenment) in each period due to the different capacity to accept a teaching (機根 Cn: jīgēn; Jp: kikon) of the people born in each respective period.

Further, in the Mahasamnipata Sutra

Mahasamnipata Sutra

The Mahāsaṃnipāta Sutra is a Buddhist text of Mahayana Buddhism. The meaning in English is the Sutra of the Great Assembly. The sutra was translated into Chinese by Dharmakṣema, beginning in the year 414...

, the three periods are further divided into five five-hundred year periods (五五百歳 Cn: wǔ wǔ bǎi sùi; Jp: go no gohyaku sai), the fifth and last of which was prophesied to be when the Buddhism of Sakyamuni would lose all power of salvation and a new Buddha would appear to save the people. This time period would be characterized by unrest, strife, famine, and other, natural disasters.

The three periods and the five five-hundred year periods are described in the Sutra of the Great Assembly (大集經 Cn: dàjí; Jp: Daishutu-kyō, Daijuku-kyō, Daijikkyō, or Daishukkyō). Descriptions of the three periods also appear in other sutras, some of which ascribe different lengths of time to them (although most agree that Mappō

Mappo

The Latter Day of the Law, is one of the Three Ages of Buddhism. Mappō or Mofa , which is also translated as the Age of Dharma Decline, is the "degenerate" Third Age of Buddhism.- Tradition :...

will last for “10,000” years, though rather than a concrete figure, this merely signifies a long period of time).