In a belief system or political or philosophical theory, a tenet is a principle that is accepted as authoritative. It is one of the principles on which a belief or theory is based. For example, one of the tenets of existentialist philosophy according to Jean-Paul Sartre is, "Man is nothing else but what he makes of himself."
In religion, a tenet can be a central belief or doctrine that is proclaimed to be true without scientific proof. For instance, one of the tenets of Christianity is that Jesus was born of a virgin mother, while a main tenet of Hinduism is that one's present birth is the consequence of one's past actions in previous lives.
In a political system or government, or even a company or organization, a tenet is a core value. For example, freedom of speech is a tenet of American democracy, while the promise of top-quality customer service is a tenet of many businesses.
An individual may possess his or her own tenets, such as always looking on the bright side of things or never being late for appointments.
The word "tenet" is also used in the sports world. "Keep your eye on the ball" and "always go for the sure out" are baseball tenets, while "keep your head up" and "hit the open man" are used in basketball.