A singleton is a world order in which there is a single decision-making agency at the highest level. The singleton hypothesis is the hypothesis that Earth-originating intelligent life will eventually assume the form a singleton.
The concept of a singleton expresses an abstract idea. A singleton could take the form of world government, such as global democracy or global totalitarianism, but this need not be so. What is required for humanity to constitute a singleton is for it to behave roughly like a coherent agent.
Bostrom, Nick (2004) The future of human evolution, in Charles Tandy (ed.) Death and Anti-Death: Two Hundred Years after Kant, Fifty Years after Turing, vol. 2, Palo Alto, California: Ria University Press, pp. 339–371.
Bostrom, Nick (2006) What is a singleton?, Linguistic and Philosophical Investigations, vol. 5, pp. 48–54.
Bostrom, Nick (2014) Superintelligence: Paths, Dangers, Strategies, Oxford: Oxford University Press, pp. 104–107.
Bostrom, Nick (2014) Superintelligence: Paths, Dangers, Strategies, Oxford: Oxford University Press, p. 83.
Ord Toby (2020) The Precipice: Existential Risk and the Future of Humanity, London: Bloomsbury Publishing, p. 397.