Tagging involves associating words with text, image, animation, or video as a strategy to locate, identify, or understand the content.
Tag Clouding -
Wordle - a toy for generating “word clouds” from text that you provide. The clouds give greater prominence to words that appear more frequently in the source text. You can tweak your clouds with different fonts, layouts, and color schemes.
Manyeyes - a tool from IBM that produces clouds as well as other visualizations of data that can be contributed by the user to identify pattern.