A visual cluster of words representing the frequency of the tags attached by readers to a text. Word clouds indicate the frequency of words within the text of a book or a blog (normally lexical words rather than grammatical words) as a quick indication of the content. In both cases relative frequency is reflected in the font sizes used to depict the words.
Chandler, Daniel - Munday, Rod (2011): Dictionary of Media and Communication. Oxford University Press. 420 p. See the Online Version