The word Yoga comes from Sanskrit, an ancient Indian language. It is derived from the word yuj, meaning "yoke" or "binding", and describes the union of the body, the mind, and the spirit.
This is done through the performance of poses or postures, each of which has specific physical benefits. The poses can be done quickly in succession, creating heat in the body through movement (vinyasa-style Yoga) or more slowly to increase stamina and perfect the alignment of the pose. The poses are a constant, but the approach to them varies depending on the style being practised. Classes may also include instruction on breathing, chanting, meditation or an inspirational reading by the teacher.
"Your practise" is your individual experience with Yoga as it develops over time. It is always evolving and changing so it never gets boring and, although the poses themselves do not change, your relationship to them will. Anyone can start a Yoga practise, even if you feel you are not flexible or very strong. These things will improve the longer you practise.
It is very different from a typical Western 'workout' as Yoga gives you true fitness and brings inner-strength, clarity and calm.