Classification

Sort is dividing or order by classes or categories based on one criterion or multiple criteria for classifying and going from general to specific or vice versa.

Example: 

Blood Groups

 

Blood groups are defined by the presence of antigenic components in the cell membrane of red blood cell antigens or agglutinogen the term refers to the determination is carried out with specific antibodies.

ABO System

The most important of the various systems of classification of blood based classification system ABO blood group. The four blood types covered in this classification are the A, B, AB and O. The blood cells of group A have the A antigen on the membrane, type B contains antigen B on their red blood cells, red blood cells contain antigens AB group A and group O BY lacks these antigens in erythrocytes.
Blood plasma may or may not contain antibodies or agglutinins which react with antigens A or B erythrocytes can never have antibodies against antigens in their red blood cells, as this would cause the destruction of these, however, the plasma contains antibodies against antigen A or B if they are present in the membrane of red blood cells and plasma in group A there are no anti-A antibodies, but anti-B blood group B contains antibodies to the antigen present in the red blood cells of group A, group O contains anti-A and anti-O, while the AB blood group does NOT contain any antibody.

 RH System 

 
Consists in the existence of various agglutinogens (Rh) in red blood cells. The term means that Rh positive Rh antigen is present in erythrocytes, however if none of this is said to be Rh negative, there are 6 types of Rh C, D, E, c, d, e, but only types C, D and E antigens are strong enough, to cause a reaction of Rh antibody, thus a person that contains these antigens to the combination of these will be Rh positive and you only have the antigens c, d and e are Rh negative.

Source: http://www.virtual.unal.edu.co/cursos/enfermeria/2005359/contenido/sanguineo/6.html