Harem refers to domestic spaces that are reserved for the women of the house in a Muslim family. A harem may house a man's wife or wives, their pre-pubescent male children, unmarried daughters, female domestic servants, and other unmarried female relatives. In the past, harems also enslaved concubines. In former times some harems were guarded by eunuchs who were allowed inside. The structure of the harem and the extent of monogamy or polygyny has varied depending on the family's personalities, socio-economic status, and local customs. Similar institutions have been common in other Mediterranean and Middle Eastern civilizations, especially among royal and upper-class families, and the term is sometimes used in other contexts. In traditional Persian residential architecture the women's quarters were known as andaruni, and in the Indian subcontinent as zenana.

In classical Islamic law, a concubine was a slave-woman with whom her master engaged in sexual relations. Concubinage was widely accepted by Muslim scholars in pre-modern times. Most modern Muslims, both scholars and laypersons, believe that Islam no longer permits concubinage and that sexual relations are religiously permissible only within marriage.