From Wikimedia Incubator

Stuttering is a speech disorder in which the normal flow of speech is frequently disrupted by repetitions (sounds, syllables, words, or phrases), pauses, and prolongations that differ both in frequency and severity from those of normally fluent individuals. The term stuttering is most commonly associated with the involuntary repetition, but it also encompasses the abnormal hesitation or pausing before speech, referred to by stutterers as blocks, and the prolongation of certain sounds, usually vowels. Much of what constitutes “stuttering” cannot be observed by the listener; this includes such things as sound and word fears, situational fears, anxiety, tension, shame, and a feeling of "loss of control" during speech. The emotional state of the individual who stutters in response to the stuttering often constitutes the most difficult aspect of the disorder.