What it isn't?
A lot of people misinterpret Yoga as a bunch of people bending themselves into weird positions. In fact there is a whole Yogic Science and philosophy behind it. When westerners think if Yoga they are actually thinking of a form of yoga called Hatha Yoga.
No reason to re-invent the wheel here, Wikipedia has already done an extensive job explaining what Yoga is, check it out
On this wiki you will find some specific explanations on what and how to integrate Hatha Yoga and its counterpart meditation into your day to day routine.
Related: