The term for a mother-in-law who refers to herself as "mom" is "matrilocal mother-in-law." In some cultures or families, the mother-in-law may use this term as a way to express closeness and acceptance of their son or daughter's spouse, considering them as part of the family and treating them like a son or daughter. This practice varies across cultures and individual family dynamics, and not all mother-in-laws may choose to refer to themselves as "mom." It's essential to respect each family's preferences and boundaries regarding such titles and forms of address.