From Wikipedia:
Kumari, or Kumari Devi, or Living Goddess – Nepal is the tradition of worshipping young pre-pubescent girls as manifestations of the divine female energy or devi in Hindu religious traditions. The word Kumari is derived from the Sanskrit Kaumarya, meaning "princess".[1]
In Nepal, a Kumari is a pre-pubescent girl selected from the Shakya caste or Bajracharya clan of the Nepalese Newari community. The Kumari is revered and worshipped by some of the country's Hindus as well as the Nepali Buddhists, though not the Tibetan Buddhists. While there are several Kumaris throughout Nepal, with some cities having several, the best known is the Royal Kumari of Kathmandu, and she lives in the Kumari Ghar, a palace in the center of the city. The selection process for her is especially rigorous. As of 2010, the Royal Kumari was Matina Shakya, aged four, installed in October 2008 by the Maoist government that replaced the monarchy. Unika Bajracharya, selected in April 2014 as the Kumari of Patan, is the second most important living goddess.[2][3]
A Kumari is generally chosen for one day and worshipped accordingly on certain festivals like Navaratri or Durga Puja. In Kathmandu Valley this is a particularly prevalent practice. A Kumari is believed to be the incarnation of Taleju. When her first menstruation begins, it is believed that the goddess vacates her body. Serious illness or a major loss of blood from an injury are also causes for loss of deity.
