The phrase "pure black" means the color black that is not mixed with any other colors or shades. It refers to something that is completely dark without any light or brightness. Full definition
I was shocked by the vast amount of pure black greeting me in the stores this season. (40plusstyle.com)
The area above the display panel also featured an ambient light sensor and a proximity sensor but both are almost hidden due to pure black color of the front panel. (techone3.in)
And that was for pure black and white, not the 16 shades of grey it can reproduce. (goodereader.com)