noun
a system of blood typing that categorizes blood into four main groups - A, B, AB, and O
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The ABO system is a classification system used to determine blood type based on the presence or absence of certain antigens.
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I had to get my blood tested to find out my ABO system, turns out I'm A positive.
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Dude, do you know your ABO system? I'm O negative, which is pretty rare.
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Understanding the ABO system is like decoding a secret language that reveals your blood type.