A "bulletproof" host or provider is the colloquial term for a business that will not reveal your identity, payment information, provide LEO access, respond to subpoenas, etc.
It's generally used by cyber-criminals as a "safe" vendor, though some privacy-minded individuals like this type of provider as well.
Those poor astronauts! ("Law Enforcement Officer", for anyone else not in the know).
inventing new word when we don't need one
Well, that countries law enforcement could always cut off those servers. It's usually either due to corruption or in case of russia political intent that these servers are kept online.
obligatory: https://xkcd.com/1053/ Happy ten thousand day!
Others already answered but while I'm chiming in anyway, I'm not in the hosting industry but IT security (for like ten years, say) and for me it's a very normal term. Maybe precisely because of that niche though; many of us are paranoid