血系 (xuè xì) literally combines 血 (xuè, 'blood') and 系 (xì, 'lineage' or 'system'), meaning 'bloodline'—the biological line of descent connecting individuals through shared ancestry. It emphasizes genetic continuity and is commonly used in contexts involving inheritance, pedigree, or familial origins.

This term appears frequently in animal husbandry, veterinary science, and breeding discussions—for example, when describing purebred livestock or pedigree dogs—where tracing lineage is essential for maintaining breed standards. While it can occasionally refer to human family lines in formal or literary contexts, its dominant usage is zoological or agricultural, not everyday personal conversation. Unlike the more colloquial 家族 (jiāzú, 'family') or 血缘 (xuèyuán, 'blood relationship'), 血系 carries a technical, systematic nuance, often implying documented or traceable descent.