Yoga is the science which deals with gaining intellectual balance in happiness and misery and gaining theability to think and act.
A Brief History About Yoga
History always helps to understand the subject more accurately. Here also it is helpful to consider the social, religious, mechanical and spiritual status of that time, when yoga originated.
In Patanjalis, yoga sutra, the word yoganusasanam is mentioned, which clearly indicates it is the remark of yoga text which existed prior to it, that was yoga science described by Hiranya garbha. Hiranya garbha is the first descibe to Astanga yoga.
Yoga word is used in vedic and Vedanta literature in Upanisads.
Yoga yajnyavalka also consists of detailed information about astanga yoga. Puranas are the most common source of knowledge and said to be an easy form of eduction. Agni purana, Vishnu purana, Garudha purana are the puranas, where detail description of Asana Pranayama can be seen.
The history shows us how the same principles of yoga are expressed in an easy and cxplanetory way in Bhagavad gita. It is the first book where all branches are explained. The aim of yoga is pictured in Gita. The way to get free from sorrows, The way to over come anger misery and to achieve the equilibrium are mentioned.
Hathayoga pradipika is the text in which Asana and pranayama are described in detail compared to previous literature. It is text by yogi Svatma rama. Gheranda samhita is also very useful text by great sage Gheranda. The text named Hatharatnavali was written by Srinivasa Bhatta Mahayogindra and is one of the major texts of yoga. These tests are considered to have been written between 6th and 15th centuries A.D.
Yoga is the correct answer for question of modern world regarding the healthy body, mind and spirit.