Twitter is a free social networking and micro-blogging service that was originally launched in March of 2006 and has since grown into a real-time short messaging service that works over multiple networks and devices. Twitter enables users to stay in touch and share information with each other in real time. Users can use a maximum of 140 characters per message or "tweet" as they are called. You can tweet as little or as often as you want, as long as each individual tweet does not exceed 140 characters.

Once you have joined Twitter, you can use their search tool to find specific people, companies, and their tweets. Hashtags are an effective method of allowing users to sort topics into useful categories to revisit later. Hashtags are a community-driven convention for users to provide add additional context and other relevant info to their tweets. The basic structure of a hashtag is simple: it’s the pound sign (#) followed by an acronym or word.

Twitter didn’t itself create hashtags; they were borrowed from IRCs (i.e. Internet Relay Channels such as chat rooms). Rather, the Twitter community adopted them as a means of creating "groupings" on the service without having to alter the basic service itself.

The Twitter community uses a hashtag in front of frequently used terms in order to categorize them for searches and filtering. So, when talking about an iPod for example, people might also reference "#Apple." If you’re looking for company specific news that’s happened recently or what’s being said about a company’s product, the hashtags can be very helpful.

Using hashtags to search Twitter for specific information is now even easier since the company purchased the search engine Summize in July of 2008. Twitter can now track hashtags itself at search.twitter.com. The engine tracks keywords too, which makes hashtags not quite as necessary for trend tracking as they were in the past. Nonetheless, they still possess unique advantages. For example, you know that anyone tagging their tweet with one of these acronyms means for it to get categorized within that topic. It also serves as a visual indicator to others following their Twitter stream that they’re tweeting about a particular subject.

One of the potential disadvantages of hashtags is their very popularity. Hashtags are so prevalent on Twitter these days that it can be hard to keep track of them all as well as what they mean. However, there is a resource available that can assist with this as well. Tagalus is a service that acts like a dictionary for hashtags. Tagalus enables users vote on definitions for tags if there’s more than one version. The definition with the most votes will be the one that defines the tag. If you invent any new tags or just want to help build the resource, you can send a tweet to @tagalus to suggest a meaning for a tag. The format for doing so is as follows:

@tagalus define mynewtag as a new tag that describes everything about me.