A handmaiden (or handmaid) is a personal maid or female servant. 
Domestic work 
A man might use a handmaiden as a concubine to bear his child if his wife was infertile. For example, the biblical Rachel, the childless wife of Jacob, gave her handmaid Bilhah to her husband to produce children. Jacob's first wife Leah later did the same. The Virgin Mary referred to herself as "the handmaid of the Lord" in acceptance of becoming pregnant by the Holy Spirit.
See also