What are pictures with a "cloudy" surface called?

Question

Photo

I know a stupid question,
but I don’t know the name of the wallpaper that usually happens on the lending-page, it has something like opasity on it, which partially blocks visibility so as not to distract the guest from important information.
So what are these pictures called and how to impose such an effect?

Answer 1

Usually, this is called overlay or shadow.

Answer 2

If I understand correctly, this effect is called "blur".
Photoshop has this filter. Menu Filter -> Blur Gallery and there are 5 different options.
I sometimes just overlay a gray rectangle on top, and then in the settings of this layer I increase the transparency to the desired value.