An extract on #hashtags
Because of its widespread use, hashtag was added to the Oxford English Dictionary in June 2014. The term hashtag can also refer to the hash symbol itself when used in the context of a hashtag.
Formal taxonomies can be developed from the folk taxonomy rendered machine-readable by the markup that hashtags provide; this process is called folksonomy.
The pound sign or hash symbol is often used in information technology to highlight a special meaning. (It should be noted that the words "Pound Sign" in the UK refer specifically to currency "" and not weight.) In 1970 for example, the number sign was used to denote immediate address mode in the assembly language of the PDP-11 when placed next to a symbol or a number. In 1978, Brian Kernighan and Dennis Ritchie used # in the C programming language for special keywords that had to be processed first by the C preprocessor. In the 1986 SGML standard, ISO 8879:1986 (q.v.), # is a reserved name indicator (rni) which precedes keyword syntactic literals,--e.g., the primitive content token #PCDATA, used for parsed character data. In usage predating the current meaning of hashtag, the pound sign was called the "hash symbol" in some countries outside of North America so as to avoid confusion with the UK currency symbol.
The pound sign was adopted for use within IRC networks circa 1988 to label groups and topics. Channels or topics that are available across an entire IRC network are prefixed with a hash symbol # (as opposed to those local to a server, which use an ampersand '&').
The use of the pound sign in IRC inspired Chris Messina to propose a similar system to be used on Twitter to tag topics of interest on the microblogging network. He posted the first hashtag on Twitter:
How do you feel about using # (pound) for groups. As in #barcamp [msg]?
Messinas suggestion to use the hashtag was not adopted by Twitter, but the practice took off after hashtags were widely used in tweets relating to the 2007 San Diego forest fires in Southern California.
According to Messina, he suggested use of the hashtag to make it easy for "lay" users to search for content and find specific relevant updates; they were for people who do not have the technological knowledge to navigate the site. Therefore, the hashtag "was created organically by Twitter users as a way to categorize messages." Today they are for anyone, either with or without technical knowledge, to easily impose enough annotation to be useful without needing a more formal system or adhering to many technical details.
Internationally, the hashtag became a practice of writing style for Twitter posts during the 20092010 Iranian election protests; Twitter users inside and outside Iran used both English- and Persian-language hashtags in communications during the events.
The first published use of the term "hash tag" was in a blog post by Stowe Boyd, "Hash Tags = Twitter Groupings," on August 26, 2007, according to lexicographer Ben Zimmer, chair of the American Dialect Society's New Words Committee.
Beginning July 2, 2009, Twitter began to hyperlink all hashtags in tweets to Twitter search results for the hashtagged word (and for the standard spelling of commonly misspelled words). In 2010, Twitter introduced "Trending Topics" on the Twitter front page, displaying hashtags that are rapidly becoming popular. Twitter has an algorithm to tackle attempts to spam the trending list and ensure that hashtags trend naturally.
Although the hashtag started out most popularly on Twitter as the main social media platform for this use, the use has extended to other social media sites including Instagram, Facebook, Flickr, Tumblr, and Google+.
In China, microblogs Sina Weibo and Tencent Weibo use a double-hashtag #HashName# format, since the lack of spacing between Chinese characters necessitates a closing tag. In contrast, when using Chinese characters (and orthographies with similar spacing conventions) on Twitter, users must insert spacing before and after the hashtagged element (e.g. ' # ' instead of '#') or insert a zero-width non-joiner character before and after the hashtagged element, to retain a linguistically natural appearance, such as '#'.