What is a hashtag?

[omthavertch]

A hashtag is a word or an unspaced phrase prefixed with the number sign ("#"). It is a form of metadata tag. Words in messages on microblogging and social networking services such as Twitter, Facebook, Google+ or Instagram may be tagged by putting "#" before them, either as they appear in a sentence, (e.g., "New artists announced for #SXSW2014MusicFestival") or appended to it.Hashtags make it possible to group such messages, since one can search for the hashtag and get the set of messages that contain it. A hashtag is only connected to a specific medium and can therefore not be linked and connected to pictures or messages from different platforms.