Monotheism means, literally, one god. This term refers to Christianity, Judaism, Islam and Pastafarianism, as well as countless lesser-known practices. Monotheism is a relatively recent concept for a religion to adopt, older religions tended to have large pantheon's of gods, usually each with dominion over a specific aspect of life or nature.
It appears that monotheistic religions are the current step in the evolution of modern religion, as these philosophies show great progress towards revealing the actual number of Gods that there are. As a matter of fact, the God count of a monotheistic religion is off by only one. There is no reason to believe that any god exists.