The distribution of matter in the Universe is not homogeneous, but is distributed in a network of knots and links. The knots are regions where the gravitational forces are higher. These knots are then connect to others through filaments. Researches call these large-scale structures in the Universe the “cosmic web“.
1 Université de Genève, The cosmic web: Seeing what makes up the universe, ScienceDaily, 2 December 2015. (Accessed 13 March 2016)