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.
There are four main sects of Buddhism which were centred in Tibet but spread to the surrounding Himalayan regions:
The Newar Buddhism of Nepal, which was centred in the Kathmandu valley, is older than Tibetan Buddhism and Tibetan Buddhism drew many teachings, particularly Vajarayana teachings, from Newar Buddhism as wll as teachings from Indian Buddhism
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.