Stammering refers to a condition that is characterised by disruptions and stoppages in fluency that interrupt the smooth flow and timing of speech. This may take the form of repetitions of sounds, syllables or words, or of prolongations of sounds so that words seem to be stretched out. Speech may sound forced, tense or jerky. People who stammer may avoid certain words or situations which they know will cause them difficulty. Stammering is not simply a speech difficulty but is a serious communication problem; it can undermine a person's self -esteem and confidence, and affect their interactions with others, as well as their employment and education potential.