Blood transfusion is the process of transferring blood or blood components from a donor to a recipient to restore blood volume, improve oxygen delivery, or correct coagulopathy. It is crucial in managing conditions such as trauma, surgery, or severe anaemia, as it can be life-saving. A key complication is transfusion reactions, which can range from mild allergic responses to severe hemolytic reactions, highlighting the importance of blood type compatibility and careful monitoring during the procedure.