Stars that are thousands of times larger than our Sun are called supergiant stars because of their enormous size and luminosity.

Here's a breakdown of why:

* Size: Supergiant stars are significantly larger than regular stars like our Sun. They can have radii hundreds or even thousands of times greater, making them truly gigantic celestial objects.

* Luminosity: Due to their massive size, supergiants have a much greater surface area than regular stars. This means they emit a tremendous amount of light and energy, making them incredibly luminous.

* Evolutionary Stage: Supergiants are in a late stage of stellar evolution. They have exhausted the hydrogen fuel in their core and are now fusing heavier elements, which releases even more energy.

In short, the term "supergiant" reflects the stars' exceptional size, extreme brightness, and advanced evolutionary stage.