The changeable web:

A tag cloud is a visual means of indicating the relative popularity of certain “tags” that have been applied to the content of a particular Web site. A tag is more often applied by Web users than it is by content producers. The size of each label, or tag, in the graphic above indicates the frequency with which that tag occurs. So we can see that content that has been tagged with the label “Education” occurs relatively more often than content that has been tagged with “Illustration.” Usually, each tag in the tag cloud is a hyperlink to content within a blog or other Web site. If this were a tag cloud for a real site, clicking Education, for example, would take me to all of the blog posts on the site that have to do with education.

A tag cloud is thus a useful way to illustrate graphically the popularity or frequency of one kind of content relative to another.

But more importantly, a tag cloud is responsive to user input. As more Illustration tags are added to the site, for example, the word “Illustration” in the tag cloud will increase in size.

The tag cloud reflects one primary aspect of the Web that is very different from conventional print mediums. Web content is easy to change and it can be flexible. Print, on the other hand, is relatively static. Once a book has gone to press, it is difficult, and costly, to make changes.