ahle kitab , closely translated as “People of the Book”, is the title given to‎ Jews and Christians in the Holy Quran.

‎why they called ahle kitab (People of the Book):

The term (People of the Book) itself appears in the Holy Quran 30 times. The title is such because the Holy Books, Taurat and Injil, were revealed to the respective Prophets of Jews (Yahud) and Christians (Nasara), the honorable Musa [A.s] and the honorable Isa [A.S], respectively. However, Muslims believe these Books were later distorted and tampered with by their own people, and with the revelation of the last Book, the Holy Quran, to the Last Prophet Muhammad [PBUH] and the completion and selection of the Din e Islam by Allah; these Books were rendered null and void. The true ‎basic and original teachings of these Books were incorporated by Allah in the Holy Quran making these Books invalid. There are varying opinions‎ about whether these Books currently exist in one form or another.‎

Marriage with ahle kitab (People of the Book):

This is a subject that requires deeper study, since the zabiha of the ahle kitab (People of the Book) is permitted to Muslims and the women of the ahle Kitab can be taken into nikah by Muslim men. Although, some disagree with this permissibility, because they contend that since their Book is no more, how can there be its people, the ahle Kitab (People of the Book). If people no longer live by the Book, they cannot claim to be its people or its followers, so they cannot be called ahle Kitab. Additionally, both Jews and Christians commit shirk against Allah when they hold the belief that the honorable Uzayr [A.S] and the honorable Isa [A.S] are but sons of Allah, respectively. Thus, if they commit shirk, the greatest sin, then how can they be ahle Kitab (People of the Book), because all the heavenly revealed Books prohibited shirk and taught Tauhid, along with other teachings.