Hidden text is text that is displayed in such a way as to not be easily readable. Hidden text is most commonly achieved by setting the font color to be the same as the background color, rendering the text invisible unless the user highlights it.
Hidden text can serve several purposes. Often websites use it to disguise spoilers for readers who do not wish to read that text. Hidden text can also be used to hide data from users less Internet-savvy or who are not familiar with a particular website. Hidden text can also be used to display keywords or phrases to a search engine spider that human visitors to the site do not see.