The word YOGA means "union" in Sanskrit, the language of ancient India where yoga originated. We can think of the union occurring between mind, body and spirit.
Yoga has become a very common term in the Western world today, and yoga classes can be found in virtually every town. Most Westerners identify yoga with hatha yoga.
Hatha yoga seeks to promote health and well-being through physical exercise. The regular practice of asanas, and breathing exercises (pranayama), makes the body strong, supple and healthy. It has a profound effect on the circulation and on the functioning of the inner organs, glands and nerves, keeping all systems in radiant health and leading to greater energy, better concentration, and a happier, more fulfilling life. Many common physical ailments can also be improved through the regular practice of yoga, and it is never too late or too early in life to take it up. Anyone can practice yoga

Five basic areas of practice: 
(1) Asanas, or Body Postures, 
(2) Pranayama, or Breathing exercises, 
(3) Cleansing practices, 
(4) Music and Sound Therapy, and 
(5) Deep Relaxation

The Aim of Yoga
Yoga Sutras of Patanjali, the ultimate aim of Yoga is to reach "Kaivalya" (emancipation or ultimate freedom). This is the experience of one's innermost being or "soul". Then one becomes free of chains of cause and effect which tie us to continual reincarnation. In Kaivalya one is said to exist in peace and tranquillity, having attained absolute knowledge of the difference between the spiritual which is timeless, unchanging and free of sorrows, and the material which is not.
This is considered desirable as life is analysed as ultimately full of sorrows and pain- even pleasure and joy leave pain and loss when they have gone as nothing in the material world is permanent.
Yoga is therefore a spiritual quest. However, along the path of yoga, the aspirant also gains health, happiness, tranquillity and knowledge which are indicators of progress and an encouragement to continue their practice. Buddhism and other Eastern spiritual traditions use many techniques derived from Yoga