Matte Film On LCD Displays
It is called diffuser. It homogenizes the light from the back or the edges of the display to create a homogenous apparel of the background illumination.

Alternatively it is possible, that you mean the anti glare or matte foil, which reduces specular reflection on displays.



According to your edit2, I'm quite sure, that you mean anti glare foil, which is a good choice for outdoor applications. You should also consider a rather bright background illumination, as it needs to concur with the huge amount of daylight which is reaching the eye of the  user.