Dehaze restores details thare are lost due to saturation in hazy areas due to dust, fog or other atmospheric problems.
A Dehaze slider is a part of the Tone Adjustment tools. Increasing the level of Dehaze will remove hazy areas and produce clear images. If you also select the Show in Tone Curve option, any changes made with the Dehaze slider appear on the Tone Curve.
Here is an original, unretouched landscape photo, taken on a hazy, sunny day.
Here is the same photo after applying the Dehaze slider.
Dehaze Slider in the Tone Panel