Marriage, also called matrimony or wedlock, is a culturally recognised union between people, called spouses, that establishes rights and obligations between them, as well as between them and their children, and between them and their in-laws. The definition of marriage varies around the world, not only between cultures and between religions, but also throughout the history of any given culture and religion. Over time, it has expanded and also constricted in terms of who and what is encompassed. Typically, it is an institution in which interpersonal relationships, usually sexual, are acknowledged or sanctioned. In some cultures, marriage is recommended or considered to be compulsory before pursuing any sexual activity. When defined broadly, marriage is considered a cultural universal. A marriage ceremony is called a wedding.