A speech impairment refers to an impaired ability to produce speech sounds and may range from mild to severe. It may include an articulation disorder, characterized by omissions or distortions of speech sounds; a fluency disorder, characterized by atypical flow, rhythm, and/or repetitions of sounds; or a voice disorder, characterized by abnormal pitch, volume, resonance, vocal quality, or duration.
The American Speech-Language Hearing Association (ASHA) has published its official definitions in Definitions of Communication Disorders and Variations .
Additional information is available from the National Information Center for Children and Youth with Disabilities (NICHCY) Speech and Language Impairments .
-  Definitions of Communication Disorders and Variations
-  Speech and Language Impairments