Vacuum-insulated is a general term describing the primary method of insulation for a container, and simply means there is extremely low air pressure between the walls.
Most people have heard of a Thermos or thermo-flask. These have a construction where the intermediate space between the inner and outer shell walls has been pumped down (by a vacuum pump) to a very low pressure; well below 1/1000th of normal atmospheric pressure. This gives very high insulating properties.
The Tempo cooler also has a very low pressure between the inner and outer shell walls created by vacuum pump-down. In addition, we use a semi-rigid insulating core material called Fumed Silica between the walls. This structure helps supports the and walls under low pressure and stops them from collapsing.