The Rhesus system is a blood-grouping system that is determined by a specific protein on the surface of red blood cells. It is also referred to as Rh factor. There are various synonyms that can be used for Rhesus system, including Rh blood group system, Rh factor system, D antigen system, Rhesus blood type system and Rhesus D system. Understanding the Rhesus system is important in medical situations such as pregnancy, where a difference in Rh factor between the mother and the unborn child can lead to hemolytic disease of the newborn. Awareness about the Rhesus system can also help in blood transfusion processes and organ transplantation.