Polite term for one's spouse's mother. Used both as a form of address and when referring to her in conversation.
My mother-in-law is very good at cooking.
Mother-in-law, this is just a little something for you.
Polite term for a woman who raises a child as her own, though not the biological mother. Less common than the mother-in-law sense.
She was raised by her foster mother from a young age.
Polite term for the wife of one's father who is not one's biological mother. Used in address and reference.
At first things were awkward with my stepmother, but now we get along well.