"A Yogi is a practioneer of Yoga. the word is used to refer to ascetic practitioneers of meditation in a number of Eastern religions including Jainism, Buddhism, Hinduism, and Taoism."
2. http://www.sciencedirect.com/science? Marian Garfinkel
"The code of conduct includes the practice of highest human virtues like ahimsa (noninjury) and satya (truth), and the promotion of the noblest feelings like amity and compassion" "the discipline of hatha yoga used in the studies described later was developed as a means for meditation: preparing the body and the nervoud system for stillness. Physical strength and meditation: preparing the body and the nervous system for stillness. Physical strength and stamina developed by asanas and pranayama allowed the mind to remain calm."
3. "yogin."Encyclopedia Britannica. Encyclopedia Britannica Online. Encyclopedia Britannica, 2011. Web 03 Mar 2011<http://www.britannica.com/EBchecked/topic/653443.yogin>.
This website gives you everything, from the defintion of differnt types iof yoga, who founded them and what the main practices of each are.
4. http://www.swamij.com/history-yoga.htm Georg Fuerstein
"the eightfold Yoga- also known as Raja-Yoga- taught by Patanjali in his Yoga-Sutra. This Sanskrit test is composed of just under 200 aphoristic statements, which have been commented on over and over again through the centuries. Sooner or later all serious Yoga students discover this work and have to grapple with its terse statements. The word sutre(which is related to Latin suture) means literally "thread" Here it conveys a thread of memory, an aid to memorization for students eager to retain Patanjali's knowledge and wisdom."