One of the central concepts on which the ideas presented by Jean Baudrillard in "precession of simulacra" (in Simulacra and Simulation, 1981) are built is that of simulation. Baudrillard developed his notion of symbolic trade to account for the manners in which we perceive and organize our world. Following Foucault, Baudrillard sees the world as governed by impersonal power or a system which decades control over knowledge of the world which is distributed across society.
Baudrillard identifies three orders of simulacra. The first order of simulacra is that which creates the real as distinguished from representation – the map, the novel and the painting are clearly an artificial representation of reality. Baudrillard ties this order of simulacrum to the Renaissance in which the attempt to accurately represent reality was the attempt to ratify its existence regardless of representation. The second order of simulacra according to Baudrillard is that which blurs the distinction between reality and representation. He ties this development to industrialization and mechanical reproduction (following Walter Benjamin's "Work of Art in the Age of Mechanical Reproduction") which allows for serial production of representations that eclipses the original. The original loses its meaning in relation to its copies.
The third order of simulacra is at the center of Baudrillard's "Precession of Simulacra". For Baudrillard the real is always already constructed. This imagined real, which we falsely believe to be actual reality, is what we lose when we move into the third order of simulacra, that of simulation. Simulation is a real which is shielded from the difference between reality and representation. This difference is eroded in (post)modern times while simulation eradicates actual referents and the real as separate from representation. The referent is then reproduced but only this time "free" and independent of the sing, what Baudrillard calls "hyperreality".
As long as we held the distinction between the real and its representation it was possible to hold on to the notion that the truth is in the world and not it the image. The real is constructed through its opposition with representation. But simulation breaks this distinction down and we can no longer claim that the truth is anywhere to be found in some objective world.