Monotheism is the belief in a single, universal, all-encompassing deity.
Deism is a form of monotheism in which it is believed that one god exists, but that God does not intervene in the world, beyond what was necessary for him to create it (no answering prayers or causing miracles).
Pantheism is form of monotheism which holds that the Universe is God. Some forms of this are tantamount to atheism, while others are more theistic. Panentheism is a form of monotheism that holds that God contains, but is not identical to, the Universe. This is also the view of Process theology.
In contrast, see Polytheism, which holds that there are many gods. Henotheism and Monolatrism are theological variants of polytheism. Recently some people have termed these beliefs inclustive monotheism (i.e. the belief in many gods, but the worship of just one of them.) Most monotheists would say that, by definition, monotheism is incompatible withpolytheism. This is because a belief in multiple gods does not imply the worship of multiple gods. Historically, many polytheists believe in the existence of many gods, but worshipped only one.
The Christian belief in the Trinity is traditionally considered a form of monotheism, although many Muslims and non-Trinitarian Christians (and a few Jews also) would question this classification.