All four schools of Tibetan Buddhism identify themselves as followers of Vajrayana Buddhism. The heart of Vajrayana Buddhist meditation is a system of practice that primarily involves a complex process of visualization and identification of oneself with an enlightened form that is portrayed as a meditation deity. This meditative practice is known as Lhai naljor, or 'Deity Yoga.' The Kalachakra practice is one such example. It is on the basis of an initiation ceremony that an individual is authorized in engaged in a deity yoga meditation. Every Tibetan Buddhist will have, as part of his or her daily religious practice, deity yoga mediation associated with a chosen meditation deity. The most popular practices are that of Yamantaka, Guhyasamaja, Chakrasamvara in the Geluk School, Guhyagarbha and Hayagirva in the Nyingma School, Vajrayogini and Chakrasamvara in the Kagyü School, and Chakrasamvara and Hevajra in the Sakya School. In addition there practices deities such as Avalokiteshvara, Manjushri and Tara, which are popular amongst the followers of all four schools, especially the laity.