Disfluency

To the long list of everyday afflictions that includes dry, itchy skin and restless leg syndrome, add another: speech disfluency.

Source: wiktionary

Siegel considered at some length, without resolving it, the apparent paradox between traditional views of stuttering and modern demonstrations that punishment (i.e. contingent aversive stimulation) tends to decrease disfluency.

Source: wiktionary

Disfluency is a relatively recent construct. Not until the last century did fluency with the specific meaning of ease of speaking become a subject of widespread interest; and only in the mid-twentieth century did its corollary, the absence of such a facility, become the focus of systematic empirical study.

Source: wiktionary