blood relation

This term specifies a biological connection, distinguishing it from relations by marriage (affinal kin) or legal adoption. It carries a strong connotation of genetic heritage and shared ancestry, often used in legal or formal contexts to establish inheritance rights or kinship ties.

In casual conversation, people often use the simpler term "relative," but "blood relation" is employed when the speaker needs to emphasize the biological nature of the bond, particularly to exclude in-laws or step-family members.