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.