A communication disorder is any disorder that affects an individuals ability to comprehend, detect, or apply language and speech to engage in dialogue effectively with others. The delays and disorders can range from simple sound substitution to the inability to understand or use ones native language. Diagnosis
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 those 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 ones native language. In general, communication disorders commonly refer to problems in speech (comprehension and/or expression) that significantly interfere with an individuals achievement and/or quality of life. Knowing the operational definition of the agency performing an assessment or giving a diagnosis may help.Persons who speak more than one language or are considered to have an accent in their location of residence do not have a speech disorder if they are speaking in a manner consistent with their home environment or that is a blending of their home and foreign environment. DSM-IV
According to the DSM-IV-TR, communication disorders are usually first diagnosed in childhood or adolescence, though they are not limited as childhood disorders and may persist into adulthood. They may also occur with other disorders.
Diagnosis involves testing and evaluation during which it is determined if the scores/performance are "substantially below" developmental expectations and if they "significantly" interfere with academic achievement, social interactions, and daily living. This assessment may also determine if the characteristic is deviant or delayed. Therefore, it may be possible for an individual to have communication challenges but not meet the criteria of being "substantially below" criteria of the DSM IV-TR. The DSM diagnoses do not comprise a complete list of all communication disorders, for example, auditory processing disorder is not classified under the DSM or ICD-10. The following diagnoses are included as communication disorders:

Expressive language disorder – characterized by difficulty expressing oneself beyond simple sentences and a limited vocabulary. Individuals can better understand than use language; they may have a lot to say, but have more difficulty organizing and retrieving the words than expected for their developmental stage. Mixed receptive-expressive language disorder – problems comprehending the commands of others. Stuttering – a speech disorder characterized by a break in fluency, where sounds, syllables, or words may be repeated or prolonged. Phonological disorder – a speech sound disorder characterized by problems in making patterns of sound errors (e.g., "dat" for "that"). Communication disorder NOS (not otherwise specified) – the DSM-IV diagnosis in which disorders that do not meet the specific criteria for the disorder listed above may be classified. DSM-5
The DSM-5 diagnoses for communication disorders completely rework the ones stated above.