Speech pathology student here. In school they teach us that stuttering is a single disorder with no single cause, but every person might stutter in a some ways more than others. We learn to categorize stuttering disfluencies (breaks in the flow) as follows: 1) partial word repetition, 2) whole word repetition, 3) inaudible prolongation (aka block) 4) audible prolongation These contrast with typical disfluencies, which non-stuttering people also do: - revisions - filler words - interjections The main difference is that typical disfluencies happen between words, while stuttering disfluencies happen within words, and are often accompanied by other emotional, cognitive, or physical stresses.