From Rigpa Wiki
Nangpa (Tib. ནང་པ་, Wyl. nang pa) — the word used for 'Buddhist' in Tibetan.
Sogyal Rinpoche writes:
[Nangpa means] 'inside-er': someone who seeks the truth not outside, but within the nature of mind. All the teachings and training in Buddhism are aimed at that one single point: to look into the nature of mind, and so free us from the fear of death and help us realize the truth of life.
- The Tibetan Book of Living and Dying, p. 52-53