A tag cloud (more traditionally known as a weighted list in the field of visual design) is a visual depiction of content tags used on a website. Often, more frequently used tags are depicted in a larger font or otherwise emphasized, while the displayed order is generally alphabetical. Thus both finding a tag by alphabet and by popularity is possible. Selecting a single tag within a tag cloud will generally lead to a collection of items that are associated with that tag.
The first widely known tag cloud appeared on Flickr, the photo sharing site. That implementation was based on Jim Flanagan's Search Referral Zeitgeist, a visualization of web site referrers. Tag clouds have also been popularised by Technorati, among others.
The first published appearance of a tag cloud can be attributed to the "subconcious files" in Douglas Coupland's Microserfs (1995).