host mother
A woman who hosts a student, traveler, or participant in a homestay program, providing accommodation and family life.
During my study abroad, my host mother was very kind to me.
A woman who carries and gives birth to a child for another person or couple. In Japanese, 代理母 is the more common term; ホストマザー in this sense is rare and may be influenced by English usage.
See also: 代理母
The term ホストマザー is sometimes used to mean surrogate mother, but it is not common.