'A hashtag is a word or an unspaced phrase prefixed with "
#".... Words or phrases in messages on microblogging and social networking services such as Facebook, Google+, Instagram, Twitter...may be tagged by entering "#" before them.... as they appear in a sentence'.. for example: "New artists announced for #Art Festival".
- sourced from wikipedia (21.15 GMT - 11 Sept 2014)
Hashtags helps you to find things and have become an important way to communicate online.
The hashtag, hash, or # - turns any word or group of words that directly follow it into a searchable link.
More # information available in this article: The Beginner's guide to the Hashtag.