A hashtag is a word or a phrase prefixed with the symbol #. It is a form of metadata tag. Short messages on microblogging social networking services such as Twitter, Tout, identi.ca, Tumblr, Instagram, Flickr, Google+ or Facebook may be tagged by putting "#" before important words, as in:
- #Wikipedia is an #encyclopedia that anyone can edit.
Hashtags provide a means of grouping such messages, since one can search for the hashtag and get the set of messages that contain it.
Read more about Hashtag: Origin, Style, Function, Use Outside of Social Networking Websites, In Popular Culture