A Word Cloud is a visual representation of the frequency of words used in a given text. It is typically composed of words that appear more frequently in the text, with the size of the words indicating the frequency of the words. Word Clouds can be used to quickly identify the main topics and ideas
From Wikipedia
A tag cloud is a visual representation of text data which is often used to depict keyword metadata on websites, or to visualize free form text. Tags are usually single words, and the importance of each tag is shown with font size or color. When used as website navigation aids, the terms are hyperlinked to items associated with the tag.