Hashtags first started being used in the 1970s in the context of information technology, specifically, in programming languages.
In 2007, Chris Messina, who isn’t even a Twitter employee, suggested using it on the website.
“How do you feel about using the # (pound) for groups. As in #barcamp [msg]?” Messina tweeted on August 23, 2007.
In 2009, Twitter took to the idea, and began linking all hashtags to Twitter search results for the hashtagged word or words.
Since then, hashtags have been adopted on almost all social media platforms, including Facebook, Instagram, and Tumblr.