The document discusses peer-to-peer (P2P) networks. It defines P2P as a communication method that allows direct connection between computers without a central server. There are two types of P2P networks: hybrid and pure. Hybrid P2P uses a central server to locate other nodes, while pure P2P connects nodes directly without a server. Skype is given as an example of hybrid P2P, while a Japanese earthquake information sharing network is provided as an example of pure P2P.