1984 is a dystopian novel by George Orwell that depicts a totalitarian society ruled by the Party and its leader, Big Brother. The novel follows Winston Smith, a low-ranking member of the Party who works in the Ministry of Truth, where he alters historical records to suit the Party's propaganda. Winston secretly rebels against the Party by keeping a diary, having a forbidden love affair with Julia, and joining the Brotherhood, a resistance group. However, he is eventually betrayed by O'Brien, a Party official who pretends to be a member of the Brotherhood, and is tortured and brainwashed into loving Big Brother. The novel ends with Winston's complete submission to the Party and its ideology.
Others have mentioned it's a reference to a novel. It was written in 1948, so the title was just a transposition of the numbers to pick a date some decades in the future.
There are a giant number of cultural references that came from it, like big brother, thought police, thought crime, double speak, newspeak, and several others.
Also, many people feel that a number of things in the fictional dystopian setting have come to pass, especially the government essentially gaslighting the people through the media in order to control society. So that's why you see so many references.
Like others have mentioned, it’s a book. I recommend reading it. Also another dystopian novel, “Brave New World” by Aldous Huxley. Lessons to be learned from both.
Yeah it's a running joke (which might be too real to be funny) that the world superpower countries are split on if their game plan is to follow 1984 or Brave New World