Tan·tra [ túntrə, tántrə ]
noun Definition: sacred writings of Tantrism: the sacred books of Tantrism. They were written between the 7th and 17th centuries and mostly consist of a dialogue between Shiva and his wife Shakti. [Late 18th century. < Sanskrit, "loom, warp, groundwork, system, doctrine"]
Tantra (Sanskrit: तन्त्र; "weave" denoting continuity), tantricism or tantrism is a religious philosophy according to which Shakti is usually the main deity worshipped, and the universe is regarded as the divine play of shakti and shiva. The word Tantra also applies to any of the scriptures commonly identified with the worship of Shakti. Tantra deals primarily with spiritual practices and ritual forms of worship, which aim at liberation from ignorance and rebirth. The tantric movement has influenced the Hindu, Bön, Buddhist, and Jain religious traditions. Tantra in its various forms has existed in South Asia, China, Japan, Tibet, Korea, Cambodia, Burma, Indonesia and Mongolia. Although he cautions against attempting a rigorous definition of tantra, David Gordon White offers the following definition:
Tantra is that Asian body of beliefs and practices which, working from the principle that the universe we experience is nothing other than the concrete manifestation of the divine energy of the Godhead that creates and maintains that universe, seeks to ritually appropriate and channel that energy, within the human microcosm, in creative and emancipatory ways.
According to Tibetan Buddhist Tantric practitioner Lama Thubten Yeshe:
...each one of us is a union of all universal energy. Everything that we need in order to be complete is within us right at this very moment. It is simply a matter of being able to recognize it. This is the tantric approach.
Sanskrit' (संस्कृता वाक् saṃskṛtā vāk, for short संस्कृतम् saṃskṛtam) is a classical language of India, and a liturgical language of Hinduism, Buddhism, Jainism & Sikhism.
Classical Sanskrit is the standard register as laid out in the grammar of Pāṇini, around the 4th century BCE. Its position in the cultures of South and Southeast Asia is akin to that of Latin and Greek in Europe and it has significantly influenced most modern languages of Nepal and India.
The pre-Classical form of Sanskrit is known as Vedic Sanskrit, with the language of the Rigveda being the oldest and most archaic stage preserved, its oldest core dating back to as early as 1500 BCE, qualifying Rigvedic Sanskrit as one of the oldest attestation of any Indo-Iranian language, and one of the earliest attested members of the Indo-European language family.
The corpus of Sanskrit literature encompasses a rich tradition of poetry and drama as well as scientific, technical, philosophical and Hindu religious texts. Today, Sanskrit continues to be widely used as a ceremonial language in Hindu religious rituals in the forms of hymns and mantras. Spoken Sanskrit is still in use in a few traditional institutions in India, and there are many attempts at revival.
Shakti, from Sanskrit shak - "to be able," meaning sacred force or empowerment, is the primordial cosmic energy and represents the dynamic forces that move through the entire universe.  Shakti is the concept, or personification, of divine feminine creative power, sometimes referred to as 'The Great Divine Mother' in Hinduism. On the earthly plane, Shakti most actively manifests through female embodiment and fertility - while also existing in males, in its potential, unmanifest form.
Not only is the Shakti responsible for creation, it also the agent of all change. Shakti is cosmic existence as well as liberation, its most significant form being the Kundalini-shakti, a mysterious psychospiritual force. Shakti exists in a state of svātantrya, dependence on no-one, being interdependent with the entire universe.
In Shaktism, Shakti is worshiped as the Supreme Being. However, in other Hindu traditions of Shaivism and Vaishnavism, Shakti embodies the active feminine energy Prakriti of Purusha, who is Vishnu in Vaishnavism or Shiva in Shaivism. Vishnu's female counterpart is called Lakshmi, with Parvati being the female half of Shiva.
Shiva:(pronunciation: [ʃɪ.ʋə]; Sanskrit: शिव, Śiva, lit. "Auspicious one" ; Tamil) is a major Hindu god, and one of the Trimurtis. In the Shaiva tradition of Hinduism, Shiva is seen as the supreme God. In the Smartha tradition, he is one of the five primary forms of God. 
Followers of Hinduism who focus their worship upon Shiva are called Shaivites or Shaivas (Sanskrit Śaiva). Shaivism, along with Vaiṣṇava traditions that focus on Vishnu, and Śākta traditions that focus on the goddess Devī are three of the most influential denominations in Hinduism.
Shiva is usually worshipped in the form of Shiva linga. In images, he is generally represented as immersed in deep meditation or dancing the Tandava upon maya, the demon of ignorance in his manifestation of Nataraja, the lord of the dance.
In some other Hindu denominations, Brahma, Vishnu, and Shiva represent the three primary aspects of the divine in Hinduism and are collectively known as the Trimurti. In this school of religious thought, Brahma is the creator, Vishnu is the maintainer or preserver, and Shiva is the destroyer or transformer.