Those who serve a diocese are considered “secular,” including bishops and their priests and sisters, because they confront “worldly” (Latin, “secularis”) authorities.
The word, “religious” literally means those vowed (bound) to pietical practices such as obedience and poverty. Hopefully, all priests are religious in the modern, broader sense of “acting on faith,” but the word has historically been used to refer specifically to those taking the special vows of a religious order (such as Franciscans), to which diocesan priests do not typically belong.
Of course, unlike “priests,” “nuns” are almost always religious... but that’s because a “nun” doesn’t mean what you think it does either. “Sisters” aren’t “nuns.”
Thanks for the thorough explanation… I guess I was referring to the way nuns are portrayed in public these days, where there’s hardly any “religious” nature involved in what they’re doing.
My wife actually has a cousin who is in a cloistered order, whom we visited a few times – the circumstances & ground rules were a bit strange, to say the least ;)