The current definition from the International Dyslexia Association states:

"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 that is often unexpected in relations to other cognitive abilities and the provision of effective classroom instruction.  Secondary consequences may include:  problems in reading comprehension and reduced reading experiences that can impede growth of vocabulary and background knowledge."