Hidden or Invisible Text
 

Unrelated hidden text is disguised by making it the same color as the background, using a tiny font size, or hiding it within HTML code such as "no frame" sections, alt attributes, zero-sized DIVs, and "no script" sections. People screening websites for a search-engine company might temporarily or permanently block an entire website for having invisible text on some of its pages. However, hidden text is not always spamdexing: it can also be used to enhance accessibility.

Hidden text are exist in the web page but invisible to the user or unreadable.

I think if its is used little for Enhancing Accessibility than it is fine, otherwise it is a black hat technique and search-engines might punish for that

These days hidden text is strictly considered to be spam by search engines. Never try to achieve rankings with hidden text. It spoils online reputation.