From the Theory Camp discussion of Charles Taylor's A Secular Age.
Taylor says that the early modern era created several spheres for popular action separate from the state: the economy, the public sphere, and the sovereign people. The more recent turn of events since the 1960s, which some call post-modern, has introduced a "fourth structure of simultaneity": the space of fashion. He describes this space as an example of the fourth structure, but he does not give any other examples, so I am not sure what else goes in this category.
In any case, he says the the space of fashion is "a horizontal, simultaneous mutual presence, which is not that of common action, but rather of mutual display. It matters to each one of us as we act that the others are there, as witness of what we are doing, and thus co-determiners of the meaning of our action.” (481)
All four of these structure are arenas for determining the popular will. They are also powerful forces in shaping the popular will. The sovereign people vote with their votes; the public sphere votes in opinion polls; the people in the market vote with their wallets. In the space of fashion the many individual acts of mutual regard and influence, of making and reading and reacting to personal style, vote in what is fashionable.
What makes this new arena of the social imaginary different is that style and expression are made at a very low level, at the level of individuals or close to it. Taylor thinks that the economy, public sphere, and popular sovereignty were products of the era of mass mobilization. The space of fashion, on the other hand, is a product of the current era of personal authenticity.