A half brother is a brother who shares one biological parent with you instead of two. If your mom remarries and has another son with your stepdad, that boy is your half brother because you share the same mom but have different dads. Or if your dad had a son from a previous relationship, that person is your half brother because you share the same dad but have different moms.

The “half” part refers to sharing about half the usual genetic connection that full siblings have. But many families don't think much about this distinction in daily life. After all, brothers who grow up together can develop the same closeness whether they share one parent or two. A half brother can be just as much a real brother as anyone else, playing games together, arguing over the remote, and annoying each other at the dinner table.

The term simply describes a biological relationship. It doesn't measure how much people care about each other or how close they feel. Some half brothers meet for the first time as adults and become great friends. Others grow up in the same house from birth and consider themselves simply brothers, period.