Yoga means “union” or “yoke” in Sanskrit. It is the unity of the body, breath, and mind and ultimately the spirit with the divine. Yoga can be practiced anywhere and by anyone. As one begins the hatha yoga journey he or she can hope to find improved posture, joint flexibility, strength, improved balance, improved concentration and better emotional balance. We learn the tools that allow the body to sit comfortably in a steady meditative posture. Once the body is steady, the attention can be focused on a particular object, breathing becomes effortless, the energy channels open, meditation begins.
In the broader system of yoga, there are different paths. The different paths take into consideration the different temperaments of the aspirants. There are the paths of Jnana Yoga, Karma Yoga, Bhakti Yoga and Raja Yoga. Please see the post on The Paths of Yoga for a description.