Stuttering, also known as stammering, is a speech disorder characterized externally by involuntary repetitions and prolongations of sounds, syllables, words, or phrases as well as involuntary silent pauses called blocks in which the person who stutters is unable to produce sounds.
According to adults who stutter, however, stuttering is defined as a "constellation of experiences" expanding beyond the external disfluencies that are apparent to the listener. Much of the experience of stuttering is internal and encompasses experiences beyond the external speech disfluencies, which are not observable by the listener. (Full article...)