Galaxies are not distributed randomly throughout the universe, but are grouped in graviationally bound clusters. These clusters are called poor or rich depending on how many galaxies they contain. Poor clusters are often called groups. The Milky Way is part of a poor cluster called the Local Group which contains about 50 galaxies including dwarf galaxies.
Clusters are then grouped together in superclusters which contain dozens of clusters. Superclusters are up to 30 Mpc across. Recent observations show that superclusters are arranged in sheets with huge voids in between, and that matter in the universe is arranged in a filamentary structure.