Answer:
Atheism is a lack of belief in a deity. It is not a religion. There are no tenants, dogma, rituals, books, etc.
Christians believe in the deity called "Yahweh" or simply, "God," and that he walked the earth as god incarnate as "Jesus Christ." It is a religion. There are tenants that must be followed, dogma that must be believed, rituals that must be performed, books that must be read, etc.