Although mind-wandering research is rapidly progressing, stark disagreements are emerging about what the term “mind-wandering” means. Four prominent views define mind-wandering as 1) task-unrelated thought, 2) stimulus-independent thought, 3) unintentional thought, or 4) dynamically unguided thought. Although theorists claim to capture the ordinary understanding of mind-wandering, no systematic studies have assessed these claims. Two large factorial studies present participants (n=545) with vignettes that describe someone’s thoughts and ask whether her mind was wandering, while systematically manipulating features relevant to the four major accounts of mind-wandering. Dynamics explains between four and twenty times more variance in participants’ mind-wandering judgments than other features. Our third study (n=153) tests and supports a unique prediction of the dynamic framework—obsessive rumination contrasts with mind-wandering. Our final study (n=277) used vignettes that resemble mind-wandering experiments. Dynamics had significant and large effects, while task-unrelatedness was insignificant. These results strongly align with the dynamic conception of mind-wandering.