A topic is a keyword or term associated with an article, video or image. This topic describes the item and enables you to retrive information (be it articles, videos or images) by topic.
For example an article about the Liverpool Football Club takeover could include the tags "George Gillett" and "Tom Hicks". Clicking on the tag "George Gillett" (next to the article) will bring you all the information on the site that has used that topic.
