Theism refers to the belief in a god. Some examples of theistic religions are Islam and Christianity. In Islam, this god referred to is called "Allah", and in Christianity, he is referred to as "God".
Buddhism is a non-theistic religion. This means that in Buddhism, there is no "god". Many people have the mistaken idea that because Buddhists go to temple and pray to a statue of Buddha, Buddha is the "god" they worship. This is not true. Statues of Buddha are not idols for worship, but rather objects of contemplation, and points on which one can focus their attention on.
A study of human history shows that human spiritual consciousness moves through three stages: polytheism, theism, and non-theism.
Polytheism: Primitive tribal peoples attribute different natural phenomena to the many gods and deities of the natural world.
Theism: As primitive tribal cultures become more civilised and structured, and form small societies governed by a monarch or single autocratic figure, they begin to favour the worship of a single entity that is deemed to be omniscient and omnipotent. Theistic religions usually advocate much preaching and evangelism to spread belief in this entity they call their god.
Non-theism: In its highest and most sophisticated stage, the human mind, through observation and a study of science, understands that phenomena occur as part of the order of nature, and not because of the actions of any deity.
As democracy and scientific thinking proliferate, and education levels rise, it is predicted that the non-theistic viewpoint will be increasingly favoured.