Marriage is a contract by which two people agree to live together as a couple for an extended period of time or for the rest of their lives, often with the aim of starting a family by having or adopting children.[source?]
It can be done by signing a contract before a civil authority, or civil marriage, or in a formal ceremony officiated by a religious authority.[source?]
The most common form of marriage is a legally binding heterosexual union. Some societies recognize polygamy, which includes but not limited to polygyny and polyandry. In polygyny, a man may be married to many women, while a woman may be married to many men. In Senegal, for example, nearly 47 percent of marriages are multiple.[1][better source needed]
The most common age to get married is between 25 to 30 years old. In the Western world, marriage for love is common. In some other countries, relatives may plan an arranged marriage.[source?]