The Clarity parameter allows you to adjust the luminance level of each pixel by using information from surrounding pixels.
Moving the Clarity slider adjusts primarily mid-tones and does so by adding or reducing contrast without adding noise.
Increasing Clarity to 30
Increasing Clarity improves the appearance of details in images that has an object that already has strong details but otherwise has hazy surroundings. Here is a photo with Clarity set to 0.
Now here is the same image with Clarity set to 30.
Decreasing Clarity to -60
Lowering Clarity results in a softer focus effect that is effective in personal or intimate photography. Here is a photo with Clarity set to 0.
Here is the same image with Clarity set to -60 on the Tone Panel.
Clarity Parameter in the Tone Panel