in DSM–IV–TR, any neurologically based information-processing disorder characterized by achievement that is substantially below that expected for the age, education, and intelligence of the individual, as measured by standardized tests in reading and mathematics and written material. 

In standard practice, a discrepancy of 2 standard deviations must exist between general intelligence testing scores (as measured by a standard normed IQtest) and achievement scores (as measured by a standard normed achievement test). A discrepancy of 1 to 2 deviations can be considered a learning disorder if some other special feature is present, such as a cognitive-processing disorder, a relevant mental disorder, a prominent medical disability, or exceptional absence from formal education. Major types of learning disorders are disorder of written expression, mathematics disorder, nonverbal learning disorder, and reading disorder. This term essentially is synonymous with learning disability and in DSM–5 is called specific learning disorder, a category that subsumes impairments of reading, mathematics, and written expression as specifiers rather than as distinct diagnostic entities themselves.