What is an adjustment layer and what are its unique advantages?

What will be an ideal response?

An adjustment layer does not contain an image; instead, it modifies some quality of all
the layers below it in the Layers panel. For example, a Brightness/Contrast layer will
alter the brightness and contrast of any underlying layers. One advantage of using an
adjustment layer instead of adjusting an existing layer directly is that adjustment layers
can be easily modified or even removed. Toggle the eye icon for the adjustment layer
to remove or restore the edit instantly. You can change a setting in an adjustment layer
at any time—even after the file has been saved. An adjustment layer can also be copied
and pasted into another image to apply the same settings there.