Hashtags are words or phrases prefixed with the symbol #,^[1][2] a form of metadata tag. They are used within IRC networks to identify groups and topics. Also, short messages on microblogging social networking services such as Twitter, identi.ca or Google+ may be tagged by including one or more with multiple words concatenated, e.g.:

#Wikipedia is an #encyclopedia

Searching for the string #Wikipedia will cause this word to appear in the search engine results. Such tags are case-insensitive, with CamelCase often used for readability.

Origin[link]

Hashtags first appeared and were used within IRC networks to label groups and topics. They are also used to mark individual messages as relevant to a particular group, and to mark individual messages as belonging to a particular topic or "channel".^[3] Generally channels / topics, that are available across an entire IRC network, are prepended with a hash symbol '#' (as opposed to those local to a server use an ampersand '&'). Hashtags' popularity grew concurrently with the rise and popularity of Twitter. It inspired Chris Messina to propose a similar system to be used on Twitter to tag topics of interest on the microblogging network. ^[4] He posted the alleged first post on Twitter to include what would become the "hashtag":

The first high-profile application of the hashtag was by San Diego, California resident Nate Ritter,^[6] who included #sandiegofire in his frequent posts on the October 2007 California wildfires hitting San Diego County. Internationally, the hashtag became a practice of writing style for Twitter posts during the 2009–2010 Iranian election protests, as both English and Farsi-language hashtags became useful for Twitter users inside and outside of Iran.

Beginning July 1, 2009, Twitter began to hyperlink all hashtags to search results containing all recent posts mentioning either the hashtag or the standard spelling of such words, provided that such words are written in the same order of characters. This was accentuated in 2010 with the introduction of "Trending Topics" on the Twitter front page, as highly-trafficked hashtags are featured as Trending Topics.

Function[link]

Hashtags are mostly used as unmoderated ad-hoc discussion forums; any combination of characters led by a pound sign is a hashtag, and any hashtag, if promoted by enough individuals, can "trend" and attract more individual users to discussion using the hashtag. On Twitter, when a hashtag becomes extremely popular, it will appear in the 'Trending Topics' area of a user's homepage. The trending topics can be organized by geographic area or by all of Twitter. Hashtags are neither registered nor controlled by any one user or group of users, and neither can they be "retired" from public usage, meaning that hashtags can be used in theoretical perpetuity depending upon the longevity of the word or set of characters in a written language. They also do not contain any set definitions, meaning that a single hashtag can be used for any number of purposes as espoused by those who make use of them.

Because of their loose nature, hashtags often become more recognized as associated with particular topics of discussion based upon a more-specific spelling of the hashtag (e.g., "#cake" as opposed to "#thecakeisalie") that will be differentiated from a more-general spelling.

Hashtags also function as beacons in order for users to find and "follow" (subscribe) or "list" (organize into public contact lists) other users of similar interest.

Use outside of social networking websites[link]

The feature has been added to other, non-short-message-oriented services, such as the user comment systems on YouTube and Gawker Media; in the case of the latter, hashtags for blog comments and directly-submitted comments are used to maintain a more constant rate of user activity even when paid employees are not logged into the website.^[7][8] Real-time search aggregators such as the former Google Real-Time Search also support hashtags in syndicated posts, meaning that hashtags inserted into Twitter posts can be hyperlinked to incoming posts falling under that same hashtag; this has further enabled a view of the "river" of Twitter posts which can result from search terms or hashtags.

Websites that support hashtags[link]

• Diaspora software and social network
• All Gawker Media websites
• Google+
• Orkut^[9]
• Tumblr
• Twitter (since 2009)
• YouTube (2009–2011)
• Instagram
• FriendFeed (since 2009)

Application[link]

Memes[link]

One phenomenon specific to the Twitter system are micro-memes, which are emergent topics for which a hashtag is created, used widely for a few days, then disappears.^[10] These hashtags also show up in a number of trending topics websites, including Twitter's own front page.

Definitions for some hashtags are available at hashtag.org. Other sites, such as Hashable, have adopted the hashtag to use for other reasons.

Promotion[link]

The hashtag phenomenon has also been harvested for advertisement, promotion and contingency coordination.

Mass broadcast media[link]

Since 2010, television series on various television channels promote themselves through "branded" hashtag bugs. This is used as a means of promoting a backchannel of online side-discussion before, during and after an episode broadcast.

While personalities associated with broadcasts, such as hosts and correspondents, also promote their corporate or personal Twitter usernames in order to receive mentions and replies to posts, usage of related or "branded" hashtags alongside Twitter usernames (e.g., #edshow as well as @edshow) is increasingly encouraged as a microblogging style in order to "trend" the hashtag (and, hence, the discussion topic) in Twitter and other search engines.

Event promotion[link]

Organized real-world events have also made use of hashtags and ad-hoc lists for discussion and promotion among participants. Hashtags are used as beacons by event participants in order to find each other on both Twitter and, in many cases, in real life during events.

Companies and advocacy organizations have taken advantage of hashtag-based discussions for promotion of their products, services or campaigns.

Political protests and campaigns in the early 2010s, such as #OccupyWallStreet and #LibyaFeb17, have been organized around hashtags or have made extensive usage of hashtags for the promotion of discussion.

In popular culture[link]

During the April 2011 Canadian party leader debate, then-Leader of the New Democratic Party, Jack Layton, referred to Conservative Prime Minister Stephen Harper's crime policies as "a hashtag fail" (presumably "#Fail").

References[link]