Pilegesh (Hebrew: פִּילֶגֶשׁ) is a Hebrew term for a concubine with similar social and legal standing to a recognized wife, often for the purpose of producing offspring.
The Torah may distinguish concubines and "sub-standard" wives with the prefix "to" (e.g., lit. "took to wives").
The term pilegesh comes from a non-Hebrew, non-Semitic loanword deriving from the Greek word pallakis (Greek παλλακίς) meaning a mistress staying in house; there is a common but unfounded view that it derives from the Aramaic phrase plag isha, meaning half-wife.
Ancient Sanskrit texts use the word "Palagali" (Sanskrit पालागलि) to denote a Sudra (out of caste) wife.
In contemporary Israeli Hebrew, the word "pilegesh" is often used as the equivalent of English "mistress"—i.e. the female partner in extramarital relations even when these relations have no legal recognition.
Several biblical figures had concubines when they were not able to create natural children with their wives. The most famous example of this was with Abraham and Sarah. Sarah, gave her maidservant Hagar to Abraham, while maintaining ownership of both maidservant and offspring. Their union produced Ishmael. Hagar gained the status of full wife in regards to Abraham, but nonetheless Sarah retained the status of main wife. Subsequently Isaac inherited Ishmael and Hagar along with the inheritance since under Hebrew law all property of a slave belongs to the master. This type of pilegesh is recorded in Jewish sources as being a singular case. All later cases of pilegesh recognized the pilegesh and guaranteed similar rights in the house as the legitimate wife. Since having children in Judaism was considered a great blessing, legitimate wives often gave their maids to their husbands so they could have children with them when those women themselves where childless, as in the cases of Leah and Zilpah; and Rachel and Bilhah. The concubine commanded the same respect and inviolability as the wife, and it was regarded as the deepest dishonor for the man to whom she belonged if hands were laid upon her. Even in the exceptional case of Sarah and Hagar, Abraham would have been obligated to treat Hagar as a full wife and she would have been treated as an equal by Abraham. Sarah's rights would have been regarding the technical legal status of being considered the inheritor and since the other wife and offspring would have been hers by ownership she became the legal albeit not biological mother of Ishmael.