Hidden text is one of the oldest black hat SEO techniques to improve the ranking of a site. The hidden text, which is also known as invisible or fake text, is the content that your visitors can’t see but the search engine can read or see that content.
Using hidden text to improve the ranking of a webpage is against the guidelines of search engines. The search engines can detect the hidden text in a webpage and treats it as spam and can ban your site temporarily or permanently. So it should be avoided by the SEOs.