Left: In traditional random networks most nodes have a medium node degree. The degrees of all nodes are distributed around the average.
Right: Real networks usually show a skewed node-degree distribution in which most nodes have only few links but, by contrast, there exist some nodes which are extremely linked. This heavy tailed distribution is known as power-law or scale-free distribution.
Node degree: The degree of a node in a network is the number of links to other nodes.
