Viniyoga is a comprehensive and authentic transmission of the teachings of yoga including āsana, prāṇāyāma, bandha, sound, chanting, meditation, personal ritual and study of texts. Viniyoga (prefixes vi and ni plus yoga) is an ancient Sanskrit term that implies differentiation, adaptation, and appropriate application.
Viniyoga: adjusting the practice of yoga to the person and to the moment.
Yoga is a state of perfect serenity, combined with perfect lucidity. The same name is used for a set of techniques, including physical positions or movements, certain breathing techniques, concentration, and meditation, which are used to help the practitioner to approach this state of yoga.
Everyone is different. Each person is unique. What is good for someone may not be good for someone else. Yoga techniques are powerful, they are excellent! We take the most advantage of them when they are adapted to each person, at that moment.
When transmitting yoga, we should consider who we are working with. What we offer should be built carefully for that person (it should not be applied to someone else, because another person will be different) and should not be always the same work, because the person changes in time, changes with the seasons, with the activity, etc.
This careful application of the Yoga techniques is called Viniyoga.