"Mantrailing" means the "search for humans based on their scent trail". Everyone permanently loses skin parts, hair and other smallest scent particles that make up an individual scent trail. This track is imperceptible to humans, but for the much more sensitive dog's nose it is no problem. With appropriate training, almost every dog is able to follow a human trace and to distinguish it from the traces of other people and even older tracks of the same person.
Mantrailing as a kind of "nose work" for dogs is therefore different from "tracking" - the search for a trail caused by ground damage - and seeking - the finding of a source of scent.