A person belonging to the category of "protected people" (ahl ad-Dhimmah) in the Islamic state. Only those from the "people of the Book" (Jews and Christians) can become Dhimmis and then have certain rights, like privately worshipping according to their religion, as long as they pay the "protection money" (jizya) but are not considered citizens of the country. Their status has to be one of humiliation (Surah 9:29).
One needs to understand this term "protected people" properly. Protected from whom? From the Muslims! It is the same dynamic as when the mafia comes to a shop owner and tells him, from now on we are protecting you, and you are going to pay us such amount of money for this protection. You will not have to bear a weapon yourself. We take that responsibility.
Details on this state of affairs in Islamic Shari'ah, Islamic history and present reality can be found here: