Yoga
Yoga is a group of ancient spiritual practices originating in India. As a general term in Hinduism it has been defined as referring to "technologies or disciplines of asceticism and meditation which are thought to lead to spiritual experience and profound understanding or insight into the nature of existence." Outside India, Yoga is mostly associated with the practice of asanas (postures) of Hatha Yoga or as a form of exercise, although it has influenced the entire dharmic religions family and other spiritual practices throughout the world.
Hindu texts discussing different aspects of yoga include the Upanishads, the Bhagavad Gita, the Yoga Sutras of Patanjali, the Hatha Yoga Pradipika, the Shiva Samhita, and many others.
Major branches of Yoga include: Hatha Yoga, Karma Yoga, Jnana Yoga, Bhakti Yoga, and Raja Yoga. Raja Yoga, known simply as Yoga in the context of Hindu philosophy, is one of the six orthodox schools of thought, established by the Yoga Sutras of Patanjali.
Yoga and Tantra
Tantrism, is a practice that is supposed to alter the relation of the individual practitioner of Tantrism to the ordinary social, religious, and logical reality in which he or she lives. Through Tantric practice an individual perceives reality as maya, illusion, and the individual achieves liberation from it.
This particular path to salvation among the several offered by Hinduism, links Tantrism to those Dharmic practices such as yoga, meditation, and social renunciation, which are based on temporary or permanent withdrawal from social relationships and modes.
During tantric practices and studies, the student is instructed further in meditation technique, particularly chakra meditation. This is often in a limited form in comparison with the way this kind of meditation is known and used by Tantric practitioners and yogis elsewhere, but is more elaborate than the initiate's previous meditation. It is considered to be a kind of Kundalini Yoga for the purpose of moving the Goddess into the chakra located in the "heart," for meditation and worship.
Goal of Yoga
Within the monist schools of Advaita Vedanta and Shaivism this perfection takes the form of Moksha, which is a liberation from all worldly suffering and the cycle of birth and death (Samsara) at which point there is a cessation of thought and an experience of blissful union with the Supreme Brahman. For the dualistic bhakti schools of Vaishnavism, bhakti itself is the ultimate goal of the yoga process, wherein perfection culminates in an eternal relationship with Vishnu or one of his associated avatars such as Krishna or Rama.
Source : http://en.wikipedia.org