What is P2P ?Edit
Generally, a peer-to-peer (or P2P) computer network refers to any network that does not have fixed clients and servers, but a number of autonomous peer nodes that function as both clients and servers to the other nodes on the network. This model of network arrangement is contrasted with the client-server model (that was unable to scale up to todays necessities). In the P2P model any node should be able to initiate or complete any supported transaction. Peer nodes may differ in local configuration, processing speed, network bandwidth, and storage quantity. This is the basic definition any p2p system.
The term P2P may mean different things to different people in different contexts. For instance, although the term has been applied to Usenet and IRC in all their incarnations and is even applicable to the network of IP hosts known as the Internet, it is most often used restricted to the networks of peers developed starting in the late 1990s characterized by transmission of data upon the receiver's request instead of the sender's. Such early networks included Gnutella, FastTrack, and the now-defunct Napster which all provide facilities for free (and somewhat anonymous) file transfer between personal computers connected in a dynamic and unreliable way to a network in order to work collectively towards a shared objective.
Even those early Networks did work around the same concept or implementation. In some Networks, such as Napster, OpenNap or IRC, the client-server structure is used for some tasks (e.g. searching) and a peer-to-peer structure for others, and even that is not consistent in each. Networks such as Gnutella or Freenet, use a peer-to-peer structure for all purposes and are sometimes referred to as true peer-to-peer networks, even though some of the last evolution are now making them into a hybrid approach were each peer is not equal in its functions.
When the term peer-to-peer was used to describe the Napster network, it implied that the peer protocol nature was important, but in reality the great achievement of Napster was the empowerment of the peers (ie, the fringes of the network). The peer protocol was just a common way to achieve this.
So the best approach will be to define peer-to-peer, not as a set of strict definitions but to extend it to a definition of a technical/social/cultural movement, that attempts to provide a decentralized, dynamic and self regulated structure (in direct opposition to the old model o central control or server-client model, that failed to scale up to today's expectations), with the objective of providing content and services. In this way a computer programs/protocol that attempts to escape the need to use a central servers/repository and aims to empower or provide a similar level of service/access to a collection of similar computers can be referred to as being a P2P implementation, and it will be in fact enabling everyone to be a creator/provider, not only a consumer. Every P2P system is by definition self feeding, the more participants it has the better it will satisfy it's objectives.