Dyslexia

n. learning disability characterized by difficulty in reading and writing

Dyslexia is a specific  learning disability that manifests primarily as a difficulty with written language, particularly with reading and spelling. It is separate and distinct from reading difficulties resulting from other causes, such as deficiencies in intelligence, a non-neurological deficiency with vision or hearing, or from poor or inadequate reading instruction.
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Dyslexia is a learning disability characterized by problems in reading, spelling, writing, speaking, or listening. [more]Dyslexia - Community and Resources

Noun
1. impaired ability to learn to read
(hypernym) learning disorder, learning disability

A specific reading disability due to a defect in the higher cortical processing of graphic symbols. Dyslexia is different from reading retardation which may, for example, reflect mental retardation or cultural deprivation.