halfbrother
A half-brother is a male who shares exactly one biological parent with another person. He is related to that person through the shared parent, but does not share both parents. This distinguishes him from a full brother, who shares both parents, and from a stepbrother or adopted brother, who is related through marriage or legal adoption rather than biology.
Genetically, half-siblings on average share about 25 percent of their DNA, reflecting the single common parent.
Socially, the relationship may be as close or as distant as other siblings, depending on family history,
Terminology notes: "half-sibling" covers any gender; the specific terms "half-brother" or "half-sister" define male or female.