What is "foster mothers"

Usage examples of "foster mothers".

But my mother was long dead and I didn't keep in touch with any of my foster mothers, let alone bring them gifts.

It was custom for sons of important samurai to have foster mothers so that the natural mother could attend to her husband and to the running of his house, leaving the foster mother to concentrate on the child's upbringing, making him strong and a credit to the parents.

She had learned in school, if not actually at the manifold knees of her foster mothers, that the MegaMall was a private corporation, and that effective ownership of the world’.