Developmental Dyslexia is a condition which causes difficulty with reading and writing. It is a learning disability that is likely present from birth. Its standard definition is a difficulty in reading and writing in spite of normal development of intelligence, cognitive and sensory abilities.
The word "dyslexia" comes from the Greek words δυς- dys- ("difficulty with") and λέξις lexis ("words" or "lexicon"). It is a brain-based condition with biochemical and genetic markers. People are identified as dyslexic when their reading or writing problems cannot be explained by a lack of intellectual ability, inadequate instruction, or sensory problems such as poor eyesight.
The term dyslexia is also sometimes used to refer to the the loss of reading ability following brain damage. This form of dyslexia is more often referred to as either acquired dyslexia or "Alexia". Dyslexia primarily impacts reading and writing abilities; however, other difficulties have been identified including deficits in processing spoken language as well as non-language difficulties.
Dyslexia is not limited to reversing the order of letters in reading or writing. Nor is it a visual perception deficit that involves reading letters or words backwards or upside down, as is often implied in popular culture.