As described on Wikipedia's Tag Cloud page:
In the first type, size represents the number of times that tag has been applied to a single item. This is useful as a means of displaying metadata about an item that has been democratically 'voted' on and where precise results are not desired. A good example of this is Last.fm, which uses this method as a means of displaying the genre with which an artist or track has been tagged.
In the second, more commonly used type, size represents the number of items to which a tag has been applied, as a presentation of each tag's popularity. Examples of this type of tag cloud are used on the image-hosting service Flickr and the blog aggregator Technorati.
In the third type, tags are used as a categorization method for content items. Tags are represented in a cloud where larger tags represent the quantity of content items in that category.
The TagCloudPlugin is an implementation of the second type described above.
The TagCloudPlugin provides a display of all available tags, displayed either as a tag cloud, or in various other ways.
The display of the generated output is dictated entirely by the CSS stylesheet. There are seven selectors in the jspwiki.css stylesheet: .tagcloud, .tagcloud a, .tagcloud .s1, .tagcloud .s2, .tagcloud .s3, .tagcloud .s4, .tagcloud .s5, the last five corresponding to color and size changes for the five tag incidence levels.
The default output:
[{TagCloud}]
Excluding all tags beginning with "P" (or "p"):
[{TagCloud exclude='[Pp].*'}]
Excluding all tags having only a single incidence:
[{TagCloud mincount='2'}]
Excluding all tags having only a single incidence and all tags beginning with "P" (or "p"):
[{TagCloud mincount='2' exclude='[Pp].*'}]
Displayed as a comma-separated list:
[{TagCloud output='comma'}]