Navigation mesh
Also said as Navmesh, Funnel algorithm
A set of flat polygons covering every place a character can walk. Search runs over the polygons rather than thousands of squares, and the route is then pulled tight round corners.
A grid wastes memory on open space, and paths on it turn in stiff right angles. A navmesh describes any shape of floor, including slopes and stairs, with far fewer nodes.
Say it
“Bake a navmesh with a 40 cm agent radius and mark doors as links, so guards take doors rather than trying to walk through the wall beside them.”
Where you’ve seen it
Mikko Mononen's open-source Recast builds navmeshes automatically from level geometry, and Unreal and Godot both use it. He also published the "simple stupid funnel" this toy uses.
Not to be confused with collision mesh
A collision mesh says what is solid. A navmesh says where a character is allowed to stand, usually shrunk in from walls by the character's radius.