wife's family; wife's parents' home
Refers to the family or home of one's wife, especially from the husband's perspective. Often used in contexts of marriage, visits, or support from the wife's side.
He went to greet his wife's family at New Year's.
出産後、妻はしばらく里方で過ごした。
After giving birth, his wife stayed at her parents' home for a while.
Compound of 里 (sato, 'village, hometown') and 方 (kata, 'direction, side'). The exact historical derivation is uncertain, but it naturally came to mean the wife's family side.