Marriage (also called matrimony or wedlock) is a social union or legal contract between people called spouses that creates kinship. The definition of marriage varies according to different cultures, but is usually an institution in which interpersonal relationships, usually intimate and sexual, are acknowledged. Such a union is often formalized via a wedding ceremony. Many cultures limit marriage to two persons of the opposite sex, but some allow forms of polygamous marriage, and some recognize same-sex marriage. In some cultures, marriage is recommended or compulsory before pursuing any sexual activity.