matter is not distributed uniformly throughout space but is instead arranged in an intricate “cosmic web” of filaments and walls surrounding bubble-like voids. Regions with high galaxy concentrations are known as galaxy clusters whereas low density regions are termed voids.
This inhomogeneous distribution of matter is called the ?Large-scale distribution of the Universe. When the Universe is considered as whole, this distribution has a similar appearance to a spider’s web or the neural network of the brain. But it was not always like this.
After the Big Bang, when the Universe was much younger, matter was distributed homogeneously. As the Universe was evolving, gravitational pulls began to compress the matter in certain regions of space, forming the large-scale structure that we currently observe.
(via Vortex Egg).