The term hidden text refers procedure of intentionally hiding keywords.
The use of hidden text has emerged in the course of search engine optimization. Its purpose is to place texts, keywords or phrases on a web page. They do not need to have the same content and theme and not be visible to users. Before, this text was read by spiders when they crawled and thus obtained a higher position.
Hiding text is considered spam at this time and violates Google's Quality Guidelines, since it adversely affects the rights of the competition. Hidden text crediting may result in websites being removed from the search engine index and a penalty may be imposed for doing so. At this point, hidden text can be easily recognized throughout the crawl based on higher keyword density and penalized accordingly.
Hidden text is part of hidden content, which includes hiding keywords in links.
How the text is hidden
The text can be hidden in various ways. The font color can be the same as the background or placed outside the margin. The font size can be set to 0 or the text placed behind an image. Another opportunity is the use of CSS technology. The text is made invisible to the user using the "visibility: hidden" or "display: none" format alternatives. Using CSS, it is also feasible separate design and content and relocate the stylesheets to isolated files.