Definition reprinted with permission from Hood, Stephen B. (editor) available from Stuttering Foundation of America: [amazon 093338825X inline]
Used interchangeably [with dysfluency] by some clinicians and differentially by others. Some feel that the prefix "dys-" should be used where there is reasonable suspicion of "organicity" to warrant the more medical terminology. The prefix "dis-" is used to denote mislearning and more psycho-emotional components. Other clinicians opt for the term "nonfluency." In any event, the terms refer to speech which is not smooth or fluent. All speakers talk disfluently at times; i.e., they hesitate or stumble in varying degrees. All stutterers are disfluent, but not all disfluency is stuttering. For instance, "disfluency" could describe the developmental hesitations of a child learning to talk, or the disrhythmic breaks in the speech of an adult. Other disfluencies are associated with neuropathology such as the speech characteristics associated with apraxia, parkinsonism, multiple sclerosis, myasthenia gravis and others.