The word "anciens" means "old" or "former" in French. It refers to people or things that existed or were in a certain place or position in the past. Full definition
The «conflict thesis» of science and religion was born in the salons of ancien régime France, where philosophes like Voltaire and d'Alembert used it as a weapon against the Catholic Church. (firstthings.com)
At no time in ancien régime Spain — neither in the Castilian revolts of 1520 nor the Andalusian urban risings of 1648 nor in any other act of social unrest — did the populace attack the Inquisition as a religious institution. (faith.org.uk)