An atheist is a person who does not believe in the existence of any gods or deities. This belief can stem from various reasons, including a reliance on scientific explanations for the universe and a lack of evidence for religious claims. Atheism is often contrasted with theism, which is the belief in one or more gods. Atheists may identify with different philosophical perspectives, such as humanism or secularism, which emphasize reason, ethics, and human welfare without reliance on religious doctrines. Atheism can be a personal belief system or part of a broader worldview that seeks to understand life through rational thought and empirical evidence.