Think of a small case with a power supply unit and a single PCEe slot inside. You plug any regular (internal) video card of your choice in it, and connect the c

Think of a small case with a power supply unit and a single PCEe slot inside. You plug any regular (internal) video card of your choice in it, and connect the case to the main computer via TB3, making the video card available as an external video card. That's a TB enclosure. These things has been for awhile, at least since TB came out. It's not called eGPU enclosure because technically it can contain any other PCIe card, though it is almost exclusively used for video cards as other devices usually can be powered by TB cable itself.