Dyslexia is a specific learning disability that is neurological in origin. It is characterized by difficulties with accurate and/or fluent word recognition and by poor spelling and decoding abilities. These difficulties typically result from a deficit in the phonological component of language, and are unexpected, considering other cognitive abilities and the provision of effective classroom instruction. Secondary consequences may include problems in reading comprehension and reduced reading experience that can impede growth of vocabulary and background knowledge.
Adopted by the International Dyslexia Association Board of Directors, November 12, 2002. This definition is also used by the National Institute of Child Health and Human Development (NICHD).