Speech disfluencies are any of various breaks, irregularities, or utterances that are often not consistent with any specific grammatical construction and occur within the flow of otherwise fluent speech. These include, for example, words and sentences that are cut off mid-utterance, phrases that are restarted or repeated, repeated syllables, grunts or unrecognizable utterances occurring as 'fillers', and 'repaired' utterances.
Fillers are parts of speech which are not generally recognized as purposeful or containing formal meaning, usually expressed as pauses such as uh, like and er, but also extending to repairs ("He was wearing a black shirt and uh, blue pants"), and articulation problems such as stuttering. Use is normally frowned upon in mass media such as news reports or films, but they occur regularly in everyday conversation, sometimes representing upwards of 20% of "words" in conversation.
Recent linguistic research has suggested that non-pathological disfluencies may contain a variety of meaning; the frequency of "uh" and "um" in English is often reflective of a speaker's alertness or emotional state. Some have hypothesized that the time of an "uh" or "um" is used for the planning of future words; other researchers have suggested that they are actually to be understood as full-fledged function words rather than accidents, indicating a delay of variable time in which the speaker wishes to pause without voluntarily yielding control of the dialogue. There is some debate as to whether to consider them a form of white noise or as a meaning-filled part of language.
In America, since the 1980s, the word "like" has been used as a discourse marker similar to filled pauses like "um" or "uh" and is widespread among youth. For example, "I, like, don't know" instead of "I, uh, don't know" (see Valley speak for more information).