Why did muhammad refer to jews and christians as "people of the book"

Aman and woman agreed to burn down a neighbor's house in retribution for some wrong the neighbor allegedly committed against them. both the man and woman were arrested shortly after they poured gasoline on the neighbor's front porch. the man revealed to the police that he participated in the plan to ensure that nothing bad would happen to the neighbor, and that he had made an anonymous telephone call to the police alerting them to the crime, which enabled the police to arrest him and the woman in the act. the woman stated that she would not have participated if not for the man's encouragement. if the woman is charged with a conspiracy at common law to commit arson, how should she be found?