What is the difference between negative and positive blood types?

Negative and Positive blood types refer to the presence of the Rhesus D (RhD) antigen. Rhesus is the second main blood group typing after the A,B,O system.

e.g.

AB+ means the blood cells have A and B and RhD antigens present on the blood cell surface.

O- means that A and B and RhD antigens are not present on the surface of the blood cell.