Maha-vajra-bhairava, wrathful aspect of Bodhisattva Manjushri
My friend, Efendi said that Japan is famous center for studying Mantra-naya sect among Mahanaya Buddhism (See below) and thus Tibet is spot for great concern of japanese mantranaya Buddhism priests and scholars.
(I cannot deny that I am influenced by cultural bias, like buddhism attitude to hinduism, or mahanaya sect attitude to "Hinayana" (Theravada)...(for the former appeared from the latter as an antithese of the latter) so I have a bias to buddhism, as a voice of freedom against choking caste hierarchy of hinduism and extreme attitude to reverence which enhances the ignorance of populace.
Degital Dictionary of Buddhism
CONCEPT OF SAMSARA
Indians believe reincarnation, and that defines social castes while in living, if you meet misfortune unluckily and it was not by the result of your action, it means you did something bad in previous life. (This process of cause and effect is "karma")
(Monotheists tend not to believe Samsara, so they don't need Nirvana.)
BUDDHISM IS DERIVED FROM HINDUISM
Historically, the prince was born in the caste hierarchy of Hinduism as Warrior / Ruler Caste (Kshatriya), and taught a teaching that is not concentrated to specified religion. And he never write his teaching as Muhammad / Christ, or other Great Religion founders didn't. But his disciples began to write down and begin to compile it, so honestly, no one remembering texts "begin" to appear, as original teaching of Christ or Patanjali.
So Nagarjuna taught the way to help others to reach Nirvana as to help yourself. (Mahayana Buddhism), so Boddhidharma came to China and taught the way to reach Nirvana by meditation and riddles, So Padmasmbhava came from India to Tibet and taught Yoga, so Six Priests of Vikramasila Temple School and Atisa taught Tibetan Priests about the Mystery of Yogic Practice and how it can be combined to Orthodox Mahayana Teaching of "Apparent (Paramita) Method" (See below)
So almost all of Major religions began as rather patriarchial, man chauvinistic, denying worship of Shakti Worship to Life, or Sexual Goddesses and physical pleasure or discipline as inferior. So monastery isolated from ordinary living thrived in each "Fundamentalists". And hinduistic pantheon is positioned as inferior beings than buddhas and bodhisativas.
Especially, fundamentally dangerous (later yogistic?) Gods like Shiva was carefully watched and sometimes despised as Ashura (Devil) rather than Deva. (But as worship of Virgin Mary in Christianity, Great Mother cannot be ignored clumsily...)
UNREALIZATION AND VOID, NOTHINGNESS, STILLNESS
Buddhism reveres the state of "Void" called Nirvana, it is frequently equated with the concept of hinduistic "moksa" (Liberation from Cycle of Reincarnation) Europeans sometimes feel uneasiness to the concept of "Void" (Maybe as concept of Cipher from the point of view of Aristotle School, rejecting Islamic Philosophy), and sometimes it is equated with Nihilism as Schopenhauer did. And hindus are quite likely using this misconcept to their misadvantage....
My friend, Greg Stafford frequently uses word "Tantric" which meaning is unclear, and differently explained by each of sects (I think he uses this ambiguity intentionally, see below) Yogic practice, that is from Patanjali and derived from Indian Hinduism, is later development after Buddhism, but adopted and absorbed for its teaching is too fascinative for it justifies Animistic / Shamanistic, magic and cantrips, like curse to neighbors or making love portion.....and incorporated into Orthodox Patriarchical Teaching of Major Religions. (See below about the process of historical Changing in Mantra-yana sect.) So I share some feeling that "Unrealisation" is degenerated compromise to Void or Nothingness which buddhism teaches.
YOGIC PRACTICE AND BUDDHISM
Esoteric Buddhism absorbs "oppressed" practice of shamanism / animism, and tries to systemise Orthodox teaching of Mahayana Buddhism taught by Nagarjuna. (See below about Chakra and Kundalini)
Hinduism since Veda text oriented have suffered with relation from other religions like Jainism and Buddhism, etc...but highly developed philosophy and creed (like Upanishad) might not have been there without it. No one remember who Patanjali actually was (though the ancient gramatist might be same name and same person), but everyone knows he is the Founder of Yogic Tantrism.
(But I don't want to write here about why a sort of "corrupted" version of Yogism was so widespread among esoteric religion outside of India....and it needs more speculation.)
I can find several contradicting explanation for this word:
1) Compromise to animistic / shamanic religions practice of pre-Aryan Invasion
2) Shaktism, worship to Feminine Goddess, and reverence to sexual force
3) Strict Rituals to monasticism, and dedication to mentors (Guru?)
#Early Age Esoteric Buddhism
Beginning of adopting Sexual Methodology and Images, secular concern is not bad for it can be turned into energy to attain Liberation. Native shamanic / animistic practices (Like shitoism in Japan, Bon in Tibet, taoism in China, etc..) were absorbed and utilised by buddhism priests, but not oriented as a
#Middle Age Esoteric Buddhism (Japanese Shinngon and Tenndai Sect can be categorised here.)
Systemised Teaching began and disciples began to worship tutors as if they are living avatar of buddhas. Baptism to disciples and complicated rituals, a Japanese Priest perceived Mahavairocanabhisa teaching and Vajrasekhara Teaching as dualistic concept, and succeeded systemizing it as Japanese Mantra-yana text in Tang Dynasty. (Many scholars pointed out that it might be influenced from dualistic teaching of Chinese Yin and Yang.)
Dualistic Japanese Mandala, as symbols of Mahavairocanabhisa teaching and Vajrasekhara Teaching
#Late Age Esoteric Buddhism (Tantric Buddhism, Tibetan Orthodox Geluq can be categorised here.)
Yogic Practice finally incoporated with newer sutras, Yogistic materialistic concern is finally justified as a method to help people as Communion, as fundamental principle of Mahayana Buddhism by great Tsonkhapa, (from his Geluq sect, Dalai Lama line began.) he taught disciples that Vajrayana (Esoteric) is greater than Paramita (Apparent) as Sun is greater than Moon, but that only after the strict practice of Apparent (Paramita) Methodology, (Meditation, fasting, etc...), it is available. I think "tantric" can only be applied to this stage, for yogic practice is never mainstream for Eastern Asia, though its sutras can be found among many.http://mypage.direct.ca/w/wattj/Glossary.htm (In this classification of Sakya and Geluq, lesser level of tantra (Kriya -> Carya -> Yoga -> Anuttrara Yoga depends on more physical level than spiritual, though in higher level, more animistic, curses and sensual symbolism are found among higher level texts......)
Four-fold Tantra Methods Main Texts Note Kriya (Action) Tantra Carya (Ritual) Tantra Mahavairocanabhisa Sutra Maybe it can be equated with Japanese Mahavairocanabhisa Mandala.... Yoga Tantra Series of Vajrasekhara Sutra Maybe it can be equated with Japanese Vajrasekhara Mandala.... Anuttara-yoga (Highest-yoga) Tantra Father Tantra
Guhyasamaja Tantra Utpakikrama, meditating upon the symbolism of mandala, completing it. (Geluq sect considered its superiority over Mother Tantra...) Mother Tantra
Chakrasambhara Tantra, Hevajra Tantra Utpannakrama Method, sensual (sexual?) and physiological yoga. Non-separable Tantra Kalachakra Tantra
Some English and Sanskrit Glossary for Buddhism
#Artman: Spirit / Soul of humanity in Indian Cosmology.
#Brahman: Cosmic Mind, (or name of One of Trimulty of Hinduistic Pantheon)
#Esoteric Buddhism: General Term for Mantra-yana, or Vajra-yana Buddhism, it admits Worldly concern and such desire can be turned into good for Spiritual Ascension, it is a part of Mahayana Buddhism but sometimes feared or despised as dangerous and amoral.
#Hina-yana Buddhism: deragatory term to "Traditional" teaching from the point of view of Mahayana buddhists. Its practitioners usually call themselves Theravada sect.
#Kundalini: Serpentine Energy inside of human body along with backbone stream and flow. Its usage was practiced by Yogists.
#Maha-yana Buddhism: Great Vehicle teaching, which reveres boddhisattva (pre-buddha) that admit to help and liberate others as well as themselves.
#Mantra-yana Buddhism: (Mantra means "true word") Term for Esoteric Buddhism
#Mandala: Paintings or Composition mapping which describes buddhism cosmology, or each of independent entities which are worshipable. It is used by Esoteric Buddhism.
#Moksa (Mukti): Object for Eastern Asia mystical teachings to liberate from Samsara, but its interpretation and method is different in each sects and religions. (Nirvana seems to be identified with this Liberation in Buddhism.)
#Paramita Buddhism: "Apparent Method" opposite to Mantra-yana and Vajra-yana "Esoteric Teaching", it requires strict monasticism need to cut practitioners off from any of worldly attachments
#Samsara: Reincarnations of "Natural" state of Spirit in Eastern Mythic Cosmology, liberation from it is Nirvana
#Shakti: Worship to Goddess as Life Force or Sexual Energy, it is avoided by Orthodox Paramita teaching, but Esoteric Buddhism tolerates its use.
#Tantra: Vague term for some type of various teaching for Esoteric Practices in east and south Asian religion
#Vajra-yana: (Vajra means Adamant or Diamond) Another term for Esoteric Buddhism, tibetan buddhists use both term, this and "Mantra-yana" as their own sect.
#Yoga: (originally means "harness") Practice to gain control Kundalini and to use for physical and spiritual requirement, originated from India. (More accurately, it is only a part of Hatha sect of Yogism.)
Legendary King of Shambhala, Pundarika, the annotator of Kalachakra Tantra, Greatest and Last Tantric Text of Tibetan Buddhism