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

Tendai is a synthesis of various Buddhist teachings, including Mahayana, Theravada, and Vajrayana. It also incorporates elements of Taoism and Confucianism, making it a unique and diverse school of Buddhism.

The core teaching of Tendai is the concept of "three truths" or "threefold truth." These truths are the ultimate truth, the conventional truth, and the middle way. The ultimate truth refers to the ultimate nature of reality, which is beyond conceptual understanding. The conventional truth refers to the everyday reality that we experience. And the middle way is the understanding that both the ultimate and conventional truths are interconnected and interdependent.

Another important concept in Tendai is the "five periods and eight teachings." This refers to the idea that there are five periods in which the Buddha taught different teachings to suit the needs and capacities of his followers. These teachings are the Lotus Sutra, the Flower Garland Sutra, the Nirvana Sutra, the Agama Sutras, and the Correct and Equal Sutra. The eight teachings are the four noble truths, the twelve-linked chain of causation, the threefold training, the twelvefold chain of dependent origination, the six paramitas, the fourfold mindfulness, the fourfold right exertion, and the fourfold right knowledge.

Tendai also places a strong emphasis on meditation and the practice of chanting mantras. This is believed to help practitioners achieve enlightenment and connect with the ultimate truth.

One of the unique aspects of Tendai is its incorporation of Shinto and indigenous Japanese beliefs and practices. This has allowed Tendai to become deeply rooted in Japanese culture and has made it accessible to the general public.

In conclusion, Japanese Tiantai, or Tendai, is a diverse and inclusive school of Buddhism that combines various teachings and practices to help practitioners achieve enlightenment. Its emphasis on the three truths, the five periods and eight teachings, and the practice of meditation and chanting make it a unique and influential school of Buddhism in Japan.