A scale-free network, also called a power law network, describes a power or exponential relationship between the degree of connectivity a node has and the frequency of its occurrence. Scale-free networks have a long tail distribution meaning there can be nodes with a very high degree but there will also be very many with a very low degree of connectivity. Many networks have been found to have this power-law link distribution, such as in many communication and social networks, in the frequency of citations between academic papers and within the social network of Hollywood actors. The power law distribution to a network like the World Wide Web is often explained with reference to what is called preferential attachment.