The Gaufre Garnie is a waffle used as a sandwich, filled either sweet or savory, and the gridded structure of the bread is what lets it be either. A waffle batter is pressed in a hot gridded iron until the outside crisps and the inside stays tender. The deep pockets of the grid are the feature that matters: they hold a filling in place, whether that filling is whipped cream and fruit on the sweet side or cheese, ham, or a spread on the savory side. The waffle is folded over its filling or sandwiched in two layers and eaten in the hand, which puts it in the same structural category as the folded galette rather than the topped pancake.
The grid does the work that a soft bun cannot. A flat bread sheds a loose filling; the gaufre's coffered squares trap it and deliver the crisp iron-pressed edge and the soft filling together in one bite. That dual behavior is also why the sandwich runs in two directions at once: the same bread that carries chantilly and fruit will, made less sweet, carry a slice of cheese and ham, because the structure is neutral enough to swing either way. It is assembled and eaten quickly. The crisp surface softens within minutes and a moist filling will seep into the batter, so it is street and stall food, handed over on paper and eaten standing, never built to be carried far.
This is a national format rather than a regional one, and the garnie name is the broad case: the waffle as a fillable bread, the contents left open. The variations are the fillings themselves, each one frequent enough to read as its own sandwich: whipped cream alone in the plainest sweet version, the denser sugar-studded Liège style as a base of its own, a savory cheese-and-ham build on the other side. Those relatives, the loaded waffles eaten like sandwiches alongside the buckwheat galettes and wheat-flour crêpes of the same hot-iron tradition, are gathered under Crêpe & Galette Salée, and the Gaufre Garnie is the general-purpose member from which the named fillings branch.