Tagalus is looking to be the Twitter dictionary for hashtags. The services allows you to define and create new hashtags for the Twitterosphere.
For example, if you are unaware of the popular #followfriday hashtag, you can find an accurate definition of the tag on Tagalus. Tagalus is seeking to crowdsource hashtags and their definitions with the help of service users.
Page definitions include previous definitions that users have recommended, several options for adding your own definition, Flickr and Youtube results, and real-time updates of when the hashtag is used.
Don’t know what a hashtag is? Definition of a hashtag.