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 (a) task‐unrelated thought, (b) stimulus‐independent thought, (c) unintentional thought, or (d) 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 40 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 nonsignificant. These results strongly suggest that the central feature of mind‐wandering is its dynamics.