A word cloud, also known as a tag cloud or a weighted list, is a visualization of text data. The most common use of a word cloud is to show keywords or tags on websites or to visualize the most important words in a piece of text. Words are usually displayed with the size of the font proportional to its importance in the data. Thus the most prominent word in a document or piece of text becomes the most prominent word in a word cloud.
Word clouds began popping up in the early 1990s, but they became popular because of the web. Early blogs used word clouds as a navigation aid, displaying keywords that showed popular topics in the blog and providing easy links. The early incarnations of Flickr, for example, relied on word clouds.
There are many different ways to lay out a word cloud. The words can appear in alphabetical order, or they can be sorted by prominence. Often layouts are random. Font size, color or weight can be used to display relative importance. Most effective, however, is horizontal text with alphabetical sorting. This makes the word cloud easy to scan and easy to use.