1. In India and its yogas, Kriya is most known as the tradition related to
Paramahamsa Yogananda, which is a teaching consisting of meditation and
pranayama (the "bellow" system).
2. In the Tibetan tradition, there is
also a school of Yoga called Kriya, but it has little relationship to
the Indian versions. In this case Kriya Yoga is the entry level to the
higher forms of Tantra, and is called Action Tantra.