“Hash tags are words or acronyms that begin with the number sign. They are used when many people are tweeting about the same topic, or from the same event. At least one hash tag is often atop Twitter’s trending topics list. Tagalus is a service to declare the meaning of those confusing hash tags. There can be more than one version, with users voting up the best definition.
Just send a tweet @tagalus to suggest a meaning for a tag. You can also add and view tags on its site. Even better, Tagalus has an API, which accesses both getting and setting of definitions (more at our Tagalus API profile). The usefulness of hashtags could really be increased if Tagalus is integrated into popular Twitter clients, the same way automatic URL shorteners make sharing links easier.
Tagalus isn’t alone in trying to make sense of hashtags. The granddaddy is Hashtags.org, which tracks tags by popularity over time…”