A "brother-in-law" is a term used to describe the brother of one's spouse or the husband of one's sibling. This relationship is part of the extended family and can vary in closeness depending on family dynamics. In many cultures, a brother-in-law can play an important role in family gatherings and celebrations. He may also be involved in family decisions and support, similar to other family members. The relationship can be friendly or distant, influenced by personal interactions and family traditions.