When hamilton uses the word "factions," who is he referring to? what groups?

In Federalist 9 an essay made by Alexander Hamilton. He asserts that "A Firm Union will be of the utmost moment to the peace and liberty of the States, as a barrier against domestic faction." In his essay, Hamilton claims that the federalist form of government projected in the Constitution, consisting of a combination of local and national governing bodies, would protect the United States against factions because the different levels of government would prevent any faction from gaining too much power. The factions here is the political parties or people who have a common interest.