Originally: a division of people between whom blood can be transfused safely. In later use also: the type of blood characteristic of such a…

The division of people into groups having blood with specific antigenic properties; the division of blood into groups based on the presence or…

= blood group n.

any of various groups into which the blood of humans and certain other animals can be divided on the basis of specific, genetically determined…

the determination of the blood group of a person, animal, or sample of blood; (also) the result of this, the blood group itself (rare).