Actually there is no proper definition of intelligence.Every person has different definition of intelligence.
Basically,Intelligence is measured by IQ(Intelligence Quotient)
Mental Retardation: Mental retardation is a condition diagnosed before age 18 that includes below-average general intellectual function, and a lack of the skills necessary for daily living
IQ < 70 before 18 years of age is a mentally retarded person.Nobody can say that he/she possesses no or zero intelligence.
There are different categories based on IQ levels.
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IQ Range Classification
140 and over Genius or near genius
120-140 Very superior intelligence
110-120 Superior intelligence
90-110 Normal or average intelligence
80-90 Dullness
70-80 Borderline deficiency
Below 70 Definite feeble-mindedness
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2. Classification IQ Limits
Very Superior 128 and over
Superior 120-127
Bright Normal 111-119
Average 91-110
Dull Normal 80-90
Borderline 66-79
Defective 65 and below
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3.IQ Range Classification
70-80 Borderline deficiency
50-69 Moron
20-49 Imbecile
below 20 Idiot
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