Theology is the study of religion, plain and simple. Of course, religion isn’t simple, so theology covers a lot of subjects, like rituals, divine beings, the history of religions, and the concept of religious truth.
Theology is taught to priests and ministers so they can better understand their religion, and it’s also taught in non-religious colleges to anyone who is curious about the ideas and effects of religion. The first half of theology is theo-, which means god in Greek. The suffix -logy means “the study of,” so theology literally means “the study of god," but we usually expand it to mean the study of religion more broadly.