The word usually denotes a particular point of view, opinion, or belief about one or more gods or deities.

There are reasonable grounds upon which one might call every human being “religious” since we, by nature, have to adopt some sort of framework in order to bring coherence and order to the circumstances and experiences of life. Whether or not a person attends meetings, and reads books (scriptures for example), or not, his worldview affects his perception of things in exactly the same way as what is typically called religion. More on this here