Twitter hash tag #???

[Mary]

What does # mean?? Do u just write anything or does it mean something im confused :O

[Dr. Fix.X.xer]

tags in twitter are used for trending some topic.For example if SOPA is most talked about thing and you want you tweet about sopa to be featured on trend page the you add # tag with itlike this
:: @dr fixxxer #SOPA yay or nay

now when you click on the highlighted #SOPA all the tweets with same name will feature on the same page

EDIT::
Definition: The # symbol, called a hashtag, is used to mark keywords or topics in a Tweet. It was created organically by Twitter users as a way to categorize messages.
Hashtags: Helping you find interesting Tweets

* People use the hashtag symbol # before relevant keywords in their Tweet to categorize those Tweets to show more easily in Twitter Search
* Clicking on a hashtagged word in any message shows you all other Tweets in that category
* Hashtags can occur anywhere in the Tweet
* Hashtagged words that become very popular are often Trending Topics

Example: In the Tweet below, @twitter added the hashtag before the phrase "thankyousteve". The word is now a link to search results for all Tweets containing "#thankyousteve" in the message.

Using hashtags

* If you Tweet with a hashtag on a public account, anyone who does a search for that hashtag may find your Tweet
* Don't #spam #with #hashtags. Don't over-tag a single Tweet. (Best practices recommend using no more than 3 hashtags per Tweet.)
* Use hashtags only on Tweets relevant to the topic

Further Discovery and Reading

* The third party site hashtags.org offers an overview of popular hashtags used on Twitter. Find out about trends, look at small, pretty graphs, and search to see if the hashtags of your fantasies exist.

* You may also want to read this article about hashtags, which appeared in The New Yorker magazine