A blogger in Bloggers Base answer to this question in a very simple way:
The Twitter World uses “#“signs in front of “Keywords” or “Groups” and “Locations“
For Example: recently Thin Air Summit held a conference and called their Hashtag #TAS08 for Thin Air Summit 2008.
These so called # groups are called “Hashtags“
Hashtags by definition are used to create real time track records of creating groups on twitter. Placing the # sign in front of keywords or targeted groups, makes it easier to track all conversations in the twitter timeline via search.
Hashtags were most notable during the San Diego forest fires in 2007 when Nate Ritter used the hashtag “#sandiegofire” to identify his updates related to the disaster.
- BloggersBase. Retrieved 29th October 15:33 2010 http://www.bloggersbase.com/internet/twitter-what-is-a-hashtag-vs-twitter-search/