A supercluster complex is the largest known structure in the Universe, consisting of walls of gravitationally bound galaxy superclusters.
The BOSS Great Wall itself is one of the largest superstructures in the observable universe! (Though there are even larger structures known.)
It contains at least 830 visible galaxies, as well as many others that are not visible (dark galaxies).
The BOSS Great Wall is roughly 1 billion light years in diameter and has a total mass of approximately 10,000 times the Milky Way galaxy.
It consists of two elongated superclusters, two large superclusters, and several smaller superclusters as well.
In this post, you can see an illustration of galaxy superclusters and cosmic voids, similar to the structure of the BOSS Great Wall.