This is taken from teh on screen documentation
<?php wp_tag_cloud(); ?>
Displays a list of tags in what is called a 'tag cloud', where the size of each tag is determined by how many times that particular tag has been assigned to posts.
In Montezuma the different sizes of tags in the cloud is removed for a stramlined display. CSS classes are available (see Widgets/Tag Cloud in the CSS section) for applying not just different sizes but any kind of style based on popularity of a tag. Use as is or with one/some of the many parameters available, see WP Docs.
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Juggledad | Forum Moderator/Support