Scaling is changing the amount of pixels in an image. Downscaling is reducing the amount of pixels, upscaling is increasing the amount of pixels.
4K upscaling is included with virtually every product that is 4K compatible, however it is often marketed in such a way that makes you think it is a visual enhancement. But the reality is it’s just required for the product to operate to make anything less than 4K take up the whole screen.
There is a fair amount of ways the scaling can be performed however, and some definitely look better than others. So the resultant quality differs between models and brands.
Having 4K upscaling on the source device is a way to bypass terrible upscaling on the TV for example, since you only need to do it once before it’s displayed. However it is not comparable to native UHD content.
With HDMI 8k on the horizon the same will apply once devices and TV’s are readily available at the right price of course!.