The crossword solution for the term 'MOTHER IN A PEN' is SOW, which is an acronym for 'Stock of Owned Animals'. This term is used in agriculture to refer to the animals owned by a farmer or rancher. These animals are typically kept in a pen or enclosure and are cared for by the owner. The term 'mother in a pen' is often used to refer to female animals that are kept in a pen and used for breeding purposes.