The Human Collective
The Human Collective is the generalized term to describe all of humanity that exists in the far reaches of the universe. There is no centralized government that controls all humans. Practically anyone could start a new colony or found a new company and call themselves a "nation."
Nations can be founded by multiple organizations. The most dominant form of nations are Corporations. Seldomly do people not declare a corporation as their citizenry when they are employed by them. There are also the classical governments that have lost (or gained, in some cases) power since the days of Old Earth. The classical governments continue the laws and traditions of the original country in the most true-to-form way possible, unless a radical leader changes that.
Many religious groups living within governments that had once persecuted them, easily found their way to establishing their own colonies, so there are not usually any dissenters within a government system. Its so easy to establish a new colony that most do just that.
The governments that have newly been established that never existed on Old Earth are known as contemporary governments. Classical and contemporary governments typically lay claim to a whole planet or large construct. Classical and contemporary governments differ from corporations in that corporations pay their citizenry, while classical and contemporary pay their governments to serve them. Classical and contemporary governments are usually reserved for religious sects, cultists, and people who believe in a "normal" governmental system such as democracy. Corporations are rarely ever democratic, and are usually totalitarian dictatorships.
The only time governments ever convene is for establishing trade rules or the like, but there is no uniting body to connect all the different nations. The Old Earth adages and terms used to describe certain aspects of life are typically the accepted ways, and most nations adhere to the terminology and other aspects, just for the sake of uniformity.
The United Nations is the closest form of unity for all governments, as most of the commerce and industry is held in their power or connected through them.