Tendai, also known as Japanese Tiantai, is a school of Buddhism that originated in Japan in the 9th century. It is based on the teachings of the Chinese monk, Zhiyi, who founded the Tiantai school in China in the 6th century.

The name Tendai comes from the Chinese word "Tiantai", which means "Heavenly Terrace". This refers to the mountain in China where Zhiyi is said to have achieved enlightenment. In Japan, Tendai is often referred to as "Tendai-shū", which means "Tendai sect" or "Tendai school".

Tendai is considered to be a synthesis of various Buddhist teachings, including Mahayana, Theravada, and Vajrayana. It also incorporates elements of Chinese Taoism and Shintoism, the indigenous religion of Japan. This blending of different traditions is one of the unique characteristics of Tendai.

One of the key teachings of Tendai is the concept of "ichinen sanzen", which means "three thousand realms in a single moment of life". This refers to the belief that all things in the universe are interconnected and that every individual has the potential to attain enlightenment. Tendai also emphasizes the importance of meditation and the use of mantras as a means to achieve enlightenment.

Tendai also places great emphasis on the Lotus Sutra, one of the most important texts in Mahayana Buddhism. This sutra teaches that all beings have the potential to attain Buddhahood and that the Buddha nature is inherent in all things.

In addition to its philosophical teachings, Tendai also has a strong focus on ritual and ceremony. This includes chanting, reciting sutras, and performing various rituals to honor the Buddha and other deities.

Tendai has had a significant influence on Japanese culture and society, particularly in the areas of art, literature, and education. Many famous temples in Japan, such as Mount Hiei and Enryaku-ji, are associated with Tendai.

In summary, Tendai is a school of Buddhism that combines various teachings and practices from different traditions. Its emphasis on interconnectedness, the potential for enlightenment, and the Lotus Sutra make it a unique and influential school of thought in Japanese Buddhism.