There are many definitions to peer to peer technology. The following is some characteristics of P2P:
Everything except the client/server model
Network of nodes with equivalent capabilities/responsibilities (symmetrical)
Nodes are both Servers and clients called “Servents”
At wikipedia, Peer-to-Peer stands for:
A peer-to-peer (or P2P) computer network is a network that relies on the computing power and bandwidth of the participants in the network rather than concentrating it in a relatively low number of servers. P2P networks are typically used for connecting nodes via largely ad hoc connections. Such networks are useful for many purposes. Sharing content files (see file sharing) containing audio, video, data or anything in digital format is very common, and realtime data, such as telephony traffic, is also passed using P2P technology.