Kafir

Noun

1. (Islam) Infidel, pagan, non-believer; a non-Muslim aside from ahl al-kitab (Christians, Jews, etc.).
2. (Islam) Infidel, pagan, non-believer; any non-Muslim.

Shaykh Al-Islam ibn Taymiyyah (Rahimullah) v27 p264: “Whosoever does not forbid people from the deen of the Jews and Christians after the prophethood of the messenger Muhammad (saw) nor declares them kafir nor hates them, he is not a Muslim by the consensus of ALL Muslims, their scholars and the general public.”