A communication disorder is any disorder that affects somebody's ability to communicate. The delays and disorders can range from simple sound substitution to the inability to understand or use one's native language.
Disorders and tendencies included and excluded under the category of communication disorders may vary by source. For example, the definitions offered by the American Speech–Language–Hearing Association differ from that of the Diagnostic Statistical Manual 4th edition (DSM-IV).
Gleanson (2001) defines a communication disorder as a speech and language disorder which refers to problems in communication and in related areas such as oral motor function. The delays and disorders can range from simple sound substitution to the inability to understand or use their native language. In general, communications disorders commonly refer to problems in speech (comprehension and/or expression) that significantly interfere with an individual’s achievement and/or quality of life. Knowing the operational definition of the agency performing an assessment or giving a diagnosis may help.