A gizmo is a device used for a specific job. A vacuum is a gizmo that cleans the floor.
While gizmo often means an unknown object — like a thingamajig — a gizmo is any device that gets a job done. A phone is a gizmo for talking to people. A stove is a gizmo that cooks food. A hammer is a gizmo that pounds in nails. Gizmos are all man-made: a plant or animal can't be a gizmo. If you want to be an inventor, come up with an original gizmo.