Mother-In-Law Day is celebrated on October 22, 2017. It is celebrated each year on the fourth Sunday in October. A mother-in-law is the mother of a person's spouse. Two women who are mothers-in-law to each other's children may be called co-mothers-in-law.
In comedies, the mother-in-law is sometimes shown as the bane of the husband, who is married to the mother-in-law's daughter. Mothers-in-law are often stereotyped in mother-in-law jokes.
A parent-in-law is a person who has a legal affinity with another by being the parent of the other's spouse. Many cultures and legal systems impose duties and responsibilities on persons connected by this relationship. (With material from: Wikipedia)