I have seen this in 4th point, TIA https://uxplanet.org/10-beginner-tricks-to-improve-your-website-design-f26bb465f745
As used in that page, it refers to what magazine editors will call “wall of text” – that is, a solid block of text with no spaces or other design elements to break it up. It’s often taken as a sign of poor writing, as it usually means that the text in question is formatted as a single paragraph, and likely will not be read by many people.
An example of a wall of text, deliberately created as such, can be found at Reddit’s r/WallOfText.
The wall of text/grey wall effect can be avoided simply by adding white space (such as paragraph breaks) at appropriate intervals; other design elements that break up walls of text are images, “pull quotes”, headings and subheadings, or lists (bulleted or numbered) – basically, anything that's not text and breaks up the solid block.