ABO blood group system definition
Developed by Karl Landsteiner in 1904; the identification of different blood groups based on differing isoantigen markers characteristic of each blood type. (Foundation in Microbiology by Talaro and Chess)
The classification of red blood cells based on the presence or absence of A and B carbohydrate antigens. (Microbiology: An Introduction by Tortora, Funke, and Case)