Facebook is celebrating "Friends Day" around the world, showing a video to more than a billion people. And it's not at all clear why.

The company has celebrated the made up holiday – ostensibly to celebrate "the importance of connecting" – the last two years. But in 2015 and 2016 it was celebrated on 4 February, which Facebook said at the time was also its birthday, and comes two days after it is being celebrated this year.

It isn't clear how the day came about, how it is intended to help its users or what it's actually for. Facebook is celebrating by showing a video to every one of the more than a billion people who log into it each day, in which a person made up of tiny pictures of a users' friends is shown dancing around.

Gadget and tech news: In pictures Show all 25 1 /25 Gadget and tech news: In pictures Gadget and tech news: In pictures Gun-toting humanoid robot sent into space Russia has launched a humanoid robot into space on a rocket bound for the International Space Station (ISS). The robot Fedor will spend 10 days aboard the ISS practising skills such as using tools to fix issues onboard. Russia's deputy prime minister Dmitry Rogozin has previously shared videos of Fedor handling and shooting guns at a firing range with deadly accuracy. Dmitry Rogozin/Twitter Gadget and tech news: In pictures Google turns 21 Google celebrates its 21st birthday on September 27. The The search engine was founded in September 1998 by two PhD students, Larry Page and Sergey Brin, in their dormitories at California’s Stanford University. Page and Brin chose the name google as it recalled the mathematic term 'googol', meaning 10 raised to the power of 100 Google Gadget and tech news: In pictures Hexa drone lifts off Chief engineer of LIFT aircraft Balazs Kerulo demonstrates the company's "Hexa" personal drone craft in Lago Vista, Texas on June 3 2019 Reuters Gadget and tech news: In pictures Project Scarlett to succeed Xbox One Microsoft announced Project Scarlett, the successor to the Xbox One, at E3 2019. The company said that the new console will be 4 times as powerful as the Xbox One and is slated for a release date of Christmas 2020 Getty Gadget and tech news: In pictures First new iPod in four years Apple has announced the new iPod Touch, the first new iPod in four years. The device will have the option of adding more storage, up to 256GB Apple Gadget and tech news: In pictures Folding phone may flop Samsung will cancel orders of its Galaxy Fold phone at the end of May if the phone is not then ready for sale. The $2000 folding phone has been found to break easily with review copies being recalled after backlash PA Gadget and tech news: In pictures Charging mat non-starter Apple has cancelled its AirPower wireless charging mat, which was slated as a way to charge numerous apple products at once AFP/Getty Gadget and tech news: In pictures "Super league" India shoots down satellite India has claimed status as part of a "super league" of nations after shooting down a live satellite in a test of new missile technology EPA Gadget and tech news: In pictures 5G incoming 5G wireless internet is expected to launch in 2019, with the potential to reach speeds of 50mb/s Getty Gadget and tech news: In pictures Uber halts driverless testing after death Uber has halted testing of driverless vehicles after a woman was killed by one of their cars in Tempe, Arizona. March 19 2018 Getty Gadget and tech news: In pictures A humanoid robot gestures during a demo at a stall in the Indian Machine Tools Expo, IMTEX/Tooltech 2017 held in Bangalore Getty Gadget and tech news: In pictures A humanoid robot gestures during a demo at a stall in the Indian Machine Tools Expo, IMTEX/Tooltech 2017 held in Bangalore Getty Gadget and tech news: In pictures Engineers test a four-metre-tall humanoid manned robot dubbed Method-2 in a lab of the Hankook Mirae Technology in Gunpo, south of Seoul, South Korea Jung Yeon-Je/AFP/Getty Gadget and tech news: In pictures Engineers test a four-metre-tall humanoid manned robot dubbed Method-2 in a lab of the Hankook Mirae Technology in Gunpo, south of Seoul, South Korea Jung Yeon-Je/AFP/Getty Gadget and tech news: In pictures The giant human-like robot bears a striking resemblance to the military robots starring in the movie 'Avatar' and is claimed as a world first by its creators from a South Korean robotic company Jung Yeon-Je/AFP/Getty Gadget and tech news: In pictures Engineers test a four-metre-tall humanoid manned robot dubbed Method-2 in a lab of the Hankook Mirae Technology in Gunpo, south of Seoul, South Korea Jung Yeon-Je/AFP/Getty Gadget and tech news: In pictures Waseda University's saxophonist robot WAS-5, developed by professor Atsuo Takanishi Rex Gadget and tech news: In pictures Waseda University's saxophonist robot WAS-5, developed by professor Atsuo Takanishi and Kaptain Rock playing one string light saber guitar perform jam session Rex Gadget and tech news: In pictures A test line of a new energy suspension railway resembling the giant panda is seen in Chengdu, Sichuan Province, China Reuters Gadget and tech news: In pictures A test line of a new energy suspension railway, resembling a giant panda, is seen in Chengdu, Sichuan Province, China Reuters Gadget and tech news: In pictures A concept car by Trumpchi from GAC Group is shown at the International Automobile Exhibition in Guangzhou, China Rex Gadget and tech news: In pictures A Mirai fuel cell vehicle by Toyota is displayed at the International Automobile Exhibition in Guangzhou, China Reuters Gadget and tech news: In pictures A visitor tries a Nissan VR experience at the International Automobile Exhibition in Guangzhou, China Reuters Gadget and tech news: In pictures A man looks at an exhibit entitled 'Mimus' a giant industrial robot which has been reprogrammed to interact with humans during a photocall at the new Design Museum in South Kensington, London Getty Gadget and tech news: In pictures A new Israeli Da-Vinci unmanned aerial vehicle manufactured by Elbit Systems is displayed during the 4th International conference on Home Land Security and Cyber in the Israeli coastal city of Tel Aviv Getty

The video should show up at the top of the news feed when a user logs in. But there's also a special Friends Day page on which it can be viewed and shared.

On that page, the video can also be edited to remove friends and pictures that shouldn't be in there.

Mark Zuckerberg announced Friends Day on 4 February, 2015, writing on Facebook that it was a "day to celebrate friends".

"It's also Facebook's birthday, but today isn't about celebrating us," he wrote. "It's about friendship."

The post then went on to write about how important friends are – that they are not a distraction but give "meaning to our lives" and "make the world work". He thanked his users for "being part of our community of friends" and called on them to "turn today into a day to celebrate a friend".

A year later – on 4 February, 2016 – came a press release and the idea of a video, which also stitched together "special moments with your friends". That release said that "each year we recognize this day as Friends Day and invite the world to celebrate and reflect on the importance of connecting".