A hashtag is a keyword or keyword phrase that starts with a “#” pound sign and does not include any spaces or punctuation. They are used to group tweets and status updates together that cover the same subject, for example a television show, a business conference or a trend. They can be used for discovery, search, real-time public conversations on social media networks, and to add sub-text or additional meaning to short messages.
Here’s a sample from my Twitter stream.
From SurfNetParents: What Are Teens Doing Online? http://t.co/ZAwxUWAzig #parenting
— Barbara Feldman (@barbarafeldman) February 23, 2014
Hashtags trace their origins back to 2007 Twitter when #SanDiegoFire become a popular hashtag used to track information about the wildfires. In fact, I was evacuated during that fire, and found Twitter to be my best source of information, and its effectiveness was certainly enhanced because of the hashtag.
Nowadays, in most applications, #hashtags are clickable, and link to a stream of tweets (status updates, etc.) that use the hashtag. Although Twitter was the first to integrate hashtags, they are now also used on Facebook, Google+, Instagram, Pinterest and Tumblr.
In other uses, television shows and networks have started promoting hashtags so that second-screen users can share their thoughts with a community of viewers who are doing the same thing.