A more thorough explanation:

Definition: A wife is a married woman who has a lawful husband living. It can also refer to a woman who contracts an informal marriage with a man and then holds herself out to the community as being married to him, known as a common-law wife. In the past, it was also used to refer to a concubine.

Examples:

• My friend's wife is a doctor.
• John and Mary have been living together for years and consider themselves common-law husband and wife.

The first example illustrates a traditional marriage where the woman is legally married to her husband. The second example illustrates a common-law marriage where the couple has not gone through a formal marriage ceremony but still considers themselves married.

Note: The term "wife" can also be used in the context of polygamous marriages, where a man has two or more wives. However, this practice is illegal in many countries.