When used in a tweet, a hashtag is a word, or words, which have been prepended with a hash symbol (#) to assist in organizing information about them. For example, if you wanted to create a hashtag out of the word "Twitter", you'd type it as "#Twitter" (no, they aren't case-sensitive). See how simple it is? With the addition of one character, a new hashtag is born.

By using hashtags, a tweet is given additional metadata that can flow inline with the 140 characters used in it and increase it's searchability by people interested in the topic. But it's not all fun-and-games. Adding too many hashtags isn't helpful, and it's actually kind of spammy. While there's no upper-limit on how many you can use, a ballpark number would be 3-4 hashtags per tweet (plus or minus a couple).

So what does all that mean for the average user? Well, simply put, if you want to gain attention to a particular topic or if you want to make it easier for others to find the things you're tweeting about, adding a hashtag would be the way to go. Hashtags are also calculated into Twitter's trending topics, which are the most active topics of discussion occurring at any given time. The more of a particular tag that are tweeted, the more likely it is to become a trending topic.

If you're interested in finding out more about hashtags and which ones are currently trending topics you can do it in two relatively easy places:

1. Use Twitter itself. Trends are located on Twitter search (below the search field). If you're logged into Twitter, there's also a "Trending Topics" area on the sidebar, directly underneath the "Lists" area. And... if you're one of the lucky ones, Twitter has recently pushed a new "location-based trends " test to approximately 1% of it's users in the same place as the existing trends within the Twitter sidebar.

2. A third-party site that's been set up to actively monitor and display hashtags. There are plenty of resources online, and I've got a few examples of ones I've previously used below:

   • hashtags.org:

     A great starting point for finding trending topics, hashtags.org provides a simple interface to search for tags. Make sure to follow @hashtags to have your hashtags tracked.

   • wthashtag.com:

     This site uses a wiki to track trending topics and allows viewers to add a definition to the tags. WTHashtag.com lists active tags, categories, and even has it's own search bar that you can install.

   • monitter.com:

     monitter.com lets you select up to 3 hashtags to watch in real-time. It also has an option to let you choose the distance from a certain area (10-100 km or miles from a specific city, state, zip code, etc.) and only see the hashtags from that area. I like to use monitter.com to find local folks who are interested in the same things that I am based on their keywords or hashtags.

   • whatthetrend.com:

     Another website that shows hashtags in real-time, whatthetrend.com has a nice, clean page that displays the trending topics in a simple list format. Another great feature is that the hashtags are not only defined, but they can be redefined if necessary.