It's been ten years to the day since the very first hashtag was shared on Twitter.
When Chris Messina (@chrismessina) tweeted #barcamp, he couldn't have known what he was starting.
Now, an average of 125 million hashtags are shared every day on Twitter from around the world. The hashtag has become part of common vernacular, from major world events to awareness campaigns: did it even happen if it didn't get a hashtag?
The most Tweeted hashtag in 2007 was used around 9,000 times. The most-used hashtag so far in 2017 was used over 300 million times.
These are the most popular hastags of all time:
The #BlackLivesMatter hashtag is a powerful example of how a hashtag can lead a movement. It started in 2012, after a neighbourhood watch co-ordinator in Florida fatally shot an African-American 17-year-old boy, but was acquitted.
Twitter became a lifeline for one dad when #CupForBen went viral last year. The story of Marc Carter (@grumpycarter) and his autistic son Ben touched the world. Ben had been drinking from the same Tommy Tippee blue cup since he was two. But when the company stopped making the cup, Marc tweeted a picture of it with the hashtag #CupForBen, appealing to people who might have a spare. The world rallied around to find Marc another cup, which they did.
#Brexit probably doesn't need an explanation, but the UK was divided over whether or not we should leave the European Union in June 2016.
Another divisive hashtag - remember #TheDress? It seemed like the whole world had their say over whether a dress was black and blue or white and gold in February 2015. The phenomenon was later revealed as differences in human colour perception which have been the subject of ongoing scientific investigation in neuroscience and vision science.
#HeForShe went viral in 2014 when Harry Potter star Emma Watson spoke at the UN to engage men and boys in helping towards gender equality.