The Large Scale Structure of the universe, also known as the Cosmic Web, is the overall placement of mass in the volume of the universe. Clusters are within Superclusters, in turn, in surfaces (sheets, walls) and strings (Galaxy Filaments) separated by large Voids. (The term large scale structure is also occasionally used to mean one of these elements.)
A picture of the structure began with the 1989 discover of the Great Wall, a sheet of galaxies, part of growing evidence that Galaxy Clusters are not evenly distributed.
Currently, Cosmological simulations aim to produce a structure similar to that observed, i.e., show a similar large scale structure. Presumed factors include entropy, pressure, density, and Gravitational Potential.
The Lyman-Alpha Forest reveals aspects of the large scale structure, as does the mapping of distant galaxies.