Blood brother can refer to one of two things: a male related by birth, or two or more men not related by birth who have sworn loyalty to each other. This is in modern times usually done in a ceremony, known as a blood oath, where each person makes a small cut, usually on a finger, hand or the forearm, and then the two cuts are pressed together and bound, the idea being that each person's blood now flows in the other participant's veins. The act carries a risk due to blood-borne diseases. The process usually provides a participant with a heightened symbolic sense of attachment with the other participant.
