Hashtags is an advanced, but easy-to-use Twitter feature. The reason they are called hashtags is because they start with a # symbol. Here are some examples: #rejectprop8, #dragmetohell, etc #rejectprop8 is a hashtag that people used when talking about Proposition 8. Users can put “#rejectprop8″ and then other Twitter users can easily find their tweets by looking at all the #rejectprop8 tweets.

Many Twitter applications, mobile and desktop, allow users to find hashtags. Some applications call them “trends” instead of “hashtags”. Most applications will keep track of the 10 or 20 most popular hashtags at any given time, so it really lets you see what people are talking about at any given time.

When the movie Drag Me to Hell came out last week (05/29/09) in the United States, many Twitter users began talking about it, and the #dragmetohell hashtag quickly jumped to the top of the Twitter top hashtag list. When looking at the #dragmetohell hashtag, I found tweets about the movie. Some contained links to reviews, some were just tweets about the user going to the movie that night, some were tweets suggesting that their friends should go see the movie, etc.

Many celebrities that have a lot of followers are very good at starting trends a.k.a. hashtags. They will post about #something and that #something will become very popular in a short amount of time. Many of their followers will begin talking about that topic and it will become widespread very quickly.

Another advanced feature is “re-tweeting” and if celebrities re-tweet tweets from their followers and those tweets in turn contain hashtags, the topic’s popularity will in a sense compound. For example, when Blink 182 member Mark Hoppus began posting about #rejectprop8, he also re-tweeted some tweets that his followers sent about #rejectprop8, and that in turn boosted the popularity of the #rejectprop8 hashtag. Soon it was at the top of the list, and Mark tweeted about how he was amazed how fast it climbed to the top of the list.

If you’re tired of reading the news to find out what’s going on, consider checking out the Twitter trend lists. Apps that let you easily follow the trend list are Twitterific, Tweetie and Twittertrend.