"C negative" refers to a specific blood type within the Rh blood group system. It indicates that a person has the C antigen present on the surface of their red blood cells but lacks the D antigen, which is associated with the more common Rh-positive blood types. Individuals with C negative blood can donate to those with C positive or C negative blood types but may only receive blood from other C negative or C positive donors. Understanding blood types is crucial for safe blood transfusions and organ transplants, as compatibility can prevent serious medical complications.