Altruism is the principle and moral practice of concern for happiness of other human beings or other animals, resulting in a quality of life both material and spiritual. It is a traditional virtue in many cultures and a core aspect of various religious traditions and secular worldviews, though the concept of "others" toward whom concern should be directed can vary among cultures and religions. In an extreme case, altruism may become a synonym of selflessness, which is the opposite of selfishness.