a term describing a follower of a religion, philosophy, or spirituality that preaches things like denial of one's instincts and abstinence from worldly pleasures in order to attain some vaguely defined goal like "salvation" or "enlightenment"(e.g. Christianity, Islam, Buddhism, and some, but not all, forms of Judaism).
The term is mostly used by Satanists or other (non)spiritualists who believe in indulgence of the flesh. It may be used as an outright insult, a smug dismissal, etc.
"Did you hear? The Dalai Lama is doing a booksigning!"
"Meh. That's white-lighter stuff. Not my thing, man."