Himalayan Buddhism is a term used to collectively refer to the Buddhist schools of Tibet, Bhutan, and regions of Nepal, and those practiced in the Indian Himalayan regions of Ladakh, Himachel Pradesh, Sikkim and Arunachel Pradesh.
Newer Buddhism of Nepal is different from Tibetan Buddhism. The latter is Mahayana school while Newer Buddhism belongs to Theravada school. However, the northern parts of Nepal are dominated with Tibetan Buddhism influence.
All these Buddhist traditions are closely related historically and all include practices of both the Mahayana and Vajrayana traditions of Buddhism. The Buddhism of Mongolia is part of the same cultural milieu, although Mongolia is not in the Himalayan region.