Theists are people who believe in God, but don't belong to any particular fiath or cult.

Brian Webber has told me his sister and father are Theists.

Actally, theism as a classification, embraces any and all who believe in a God or gods. It's just used in the narrower way you have to indicate those monothists who do not fall into any specific subset of the broader definition, such as "Baptists," or even "Christians."

But even this description does not adequately cover the narrower use of the term, since Deists tend to be included in this narrower definition.

This is a word that would be much better served by not using it. Too awkward, too broad, Too bipolar.

Theism is used as contra both Deism and Atheism.
Theists believe God to be personal while Deists
believe in a more Impersonal God.
Of course Atheists don't believe God exists at all.