The dictionary meaning of the word atheist is one who does not believe in God. People who are atheists follow atheism.
ATHEISM MEANS rejection of belief in the existence of God. On the contrary, people following Hinduism, Islam, Buddhism, Jainism and Christianity believe in God and worship various deities. In Bible, the First Chapter traces the creation of the world. It is called genesis. Most of the tribal groups (especially in the African continent) all over the world are atheists. They have no faith in God. I wonder why? Every person has as an inner conscious. How can then one say that there is no God? In fact God has created the whole universe, and fully controls its functioning. For example, the sun rises and sets, and goes to the other world. It shines continuously. Moon also does the same, though it is not visible during the day time. It takes light from the sun and shines at night. There are a large number of people, all over the world, who have no faith in God.