父系 (fùxì) literally means 'father’s line'—it refers to the lineage traced exclusively through the father’s side of the family. The character 父 (fù) means 'father', and 系 (xì) means 'line', 'system', or 'kinship line'. Together, they form a technical term used in anthropology, genetics, and social studies to describe descent, inheritance, or group identity based on paternal ancestry.

This term appears frequently when discussing kinship systems, clan structures, or genetic inheritance patterns—especially in contexts comparing patrilineal versus matrilineal societies. In Chinese academic writing, it’s often paired with 母系 (mǔxì, 'matrilineal line'). While commonly applied to human societies, 父系 is also used in animal breeding and genetics—for example, describing inherited traits passed down only from the sire (male parent) in livestock or laboratory species.