Vajrayāna (वज्रयान), Mantrayāna, Tantrayāna, Tantric Buddhism and Esoteric Buddhism are terms referring to the various Buddhist traditions of Tantra and "Secret Mantra", which developed in medieval India and spread to Tibet, Bhutan, and East Asia. In Tibet, Buddhist Tantra is termed Vajrayāna, while in China it is generally known as Tángmì Hanmi 漢密 (唐密, "Chinese Esotericism") or Mìzōng (密宗, "Esoteric Sect"), in Pali it is known as Pyitsayãna (ပစ္စယာန) , and in Japan it is known as Mikkyō (密教, "secret teachings").
Vajrayāna is usually translated as Diamond Vehicle or Thunderbolt Vehicle, referring to the Vajra, a mythical weapon which is also used as a ritual implement.
Tantra (/ˈtʌntrə, ˈtæn-/; Sanskrit: तन्त्र, literally "loom, weave, system") denotes the esoteric traditions of Hinduism and Buddhism that co-developed most likely about the middle of the 1st millennium AD. The term tantra, in the Indian traditions, also means any systematic broadly applicable "text, theory, system, method, instrument, technique or practice".
Starting in the early centuries of common era, newly revealed Tantras centering on Vishnu, Shiva or Shakti emerged. In Buddhism, the Vajrayana tradition is known for its extensive tantra ideas and practices. Tantric Hindu and Buddhist traditions have influenced other Eastern religious traditions such as Jainism, the Tibetan Bön tradition, Daoism and the Japanese Shintō tradition.
Kālachakra refers both to a tantric deity (yidam) and to the philosophies and meditation practices contained within the Kālachakra Tantra and its many commentaries. The Kālachakra Tantra is more properly called the Kālachakra Laghutantra, and is said to be an abridged form of an original text, the Kālachakra Mūlatantra which is no longer extant. Some Buddhist masters assert that Kālachakra is the most advanced form of Vajrayana practice; it certainly is one of the most complex systems within Tantric Buddhism.
The Kālachakra tradition revolves around the concept of time (kāla) and cycles (chakra): from the cycles of the planets, to the cycles of human breathing, it teaches the practice of working with the most subtle energies within one's body on the path to enlightenment.
The Kālachakra deity represents a Buddha and thus omniscience. Since Kālachakra is time and everything is under the influence of time, Kālachakra knows all. Whereas Kālachakri or Kālichakra, his spiritual consort and complement, is aware of everything that is timeless, untimebound or out of the realm of time. In yab-yum, they are temporality and atemporality conjoined. Similarly, the wheel is without beginning or end.
The Kālachakra deity resides in the center of the mandala in his palace consisting of four mandalas, one within the other: the mandalas of body, speech, and mind, and in the very center, wisdom and great bliss. The Kālachakra sand mandala is dedicated to both individual and world peace and physical balance. The Dalai Lama explains: “It is a way of planting a seed, and the seed will have karmic effect. One doesn’t need to be present at the Kālachakra ceremony in order to receive its benefits.”
Kūkai is famous as a calligrapher (see Shodo), engineer, and is said to have invented kana, the syllabary in which, in combination with Chinese characters (Kanji) the Japanese language is written (although this claim has not been proven).
His religious writing, some fifty works, expound the esoteric Shingon doctrine, of which the major ones have been translated into English by Yoshito Hakeda (see references below). Kūkai is also said to have written the iroha, one of the most famous poems in Japanese, which uses every phonetic kana syllable.
Vajrayoginī (Sanskrit: Vajrayoginī; Tibetan: རྡོ་རྗེ་རྣལ་འབྱོར་མ་, Wylie: rdo rje rnal ’byor ma, Dorjé Neljorma; Mongolian: Огторгуйд Одогч, Нархажид, Chinese: 瑜伽空行母; pinyin: Yújiā Kōngxíngmǔ) is a Tantric Buddhist female Buddha and a ḍākiṇī. Vajrayoginī's essence is "great passion" (maharaga), a transcendent passion that is free of selfishness and illusion — she intensely works for the well-being of others and for the destruction of ego clinging. She is seen as being ideally suited for people with strong passions, providing the way to transform those passions into enlightened virtues.
She is an Anuttarayoga Tantraiṣṭadevatā (meditation deity) and her practice includes methods for preventing ordinary death, intermediate state (bardo) and rebirth (by transforming them into paths to enlightenment), and for transforming all mundane daily experiences into higher spiritual paths. Practices associated with her are Chöd and the Six Yogas of Naropa.
Vajrayoginī is often described with the epithet sarvabuddhaḍākiṇī, meaning "the ḍākiṇī who is the Essence of all Buddhas".
According to scholar Miranda Shaw, Vajrayoginī is "inarguably the supreme deity of the Tantric pantheon. No male Buddha, including her divine consort, Heruka-Cakrasaṃvara, approaches her in metaphysical or practical import."