The term “pseudo-single domain” (PSD) has been used to describe the transitional state in rockmagnetism that spans the particle size range between the single domain (SD) and multidomain (MD) states.The particle size range for the stable SD state in the most commonly occurring terrestrial magneticmineral, magnetite, is so narrow (~20–75 nm) that it is widely considered that much of the paleomagneticrecord of interest is carried by PSD rather than stable SD particles. The PSD concept has, thus, become thedominant explanation for the magnetization associated with a major fraction of particles that recordpaleomagnetic signals throughout geological time. In this paper, we argue that in contrast to the SD and MDstates, the term PSD does not describe the relevant physical processes, which have been documentedextensively using three-dimensional micromagnetic modeling and by parallel research in material scienceand solid-state physics. We also argue that features attributed to PSD behavior can be explained bynucleation of a single magnetic vortex immediately above the maximum stable SD transition size. Withincreasing particle size, multiple vortices, antivortices, and domain walls can nucleate, which producevariable cancellation of magnetic moments and a gradual transition into the MD state. Thus, while the termPSD describes a well-known transitional state, it fails to describe adequately the physics of the relevantprocesses. We recommend that use of this term should be discontinued in favor of “vortex state,” whichspans a range of behaviors associated with magnetic vortices.