1. A classification system for the antigens of human blood; used in blood transfusion therapy; four groups are A and B and AB and O
   - ABO blood group system, ABO system

Type of: classification system

• closed interval
• closed loop
• closed primary
• closed session
• closed shop
• closed universe
• closed-angle glaucoma
• closed-captioned
• closed-circuit television
• closed-class word
• closed-door
• closed-end fund
• closed-end investment company
• closed-heart surgery
• closed-loop system
• closed-minded
• closed-ring
• closedown
• closefisted
• closelipped
• closely
• closely held corporation
• closely knit
• closely-held
• closemouthed