What does your IQ really mean?

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So, I took this IQ test and I wont reveal my scores b/c i dont really know if it means im stupid or not (lol) but you know how there's a grading scale for school; For example a 89-100 is an A or a 79-89 is a B, stuff like that. So with IQ, is a grade of 43 which is an F equivalent to stupid? How does that work? Does anyone know?