'P2P or peer-to-peer technology' aka a computer network that uses the combined bandwidth of its users.
Peer-to-peer (P2P) file sharing is a system of sharing files directly between network users, without the assistance or interference of a central server. Files reside on computers of users all over the world and are shared bit by bit between those users directly. The decentralized nature of peer-to-peer file sharing removes the need for a central server, and removes the possibility of centralized control. File Sharing Software consists of software programs designed to let users download or upload files to or from other users or other groups of users.
A great heap of P2P and File sharing software can be found here.
Peer-to-peer file sharing networks are also more resistant to legal attacks, because there is no one central entity to file a lawsuit against. To attack a peer-to-peer file sharing network, a claimant must file suits against individual network users.
The community of users in a P2P network is completely responsible for deciding what content is available. Unpopular files will eventually disappear and become unavailable as more people stop sharing them. Popular files, however, will be highly and easily distributed. Popular files on a P2P network actually have more stability and availability than files on central networks. In a centralized network, only the loss of connection between the clients and server is simple enough to cause a failure, but in P2P networks, the connections between every node must be lost in order to fail to share data. In a centralized system, the administrators are responsible for all data recovery and backups, while in P2P systems, each node requires its own backup system. Because of the lack of central authority in P2P networks, forces such as the recording industry, RIAA, MPAA, and the government are unable to delete or stop the sharing of content on P2P systems.
The emergence of BitTorrent as a standard file sharing protocol has somewhat changed this in so far as tracker operators and torrent search engines have become a primary target of legal attacks, if not for actual copyright infringement then for providing the means for it.
While some of the old file sharing networks are still available bittorrent is by far the most popular, most convenient and most effective way to share files. In a nutshell, file sharers first download a small torrent file and open it with a bittorrent client. Torrent file gives the client all the information it needs to connect to other file sharers which have the pieces of the file, download them, and put them together.
But even all this doesn't come without a price.
The avalanche of negative file-sharing news over the past weeks hasn’t gone unnoticed to users and site operators. From SOPA to Megaupload, there is a growing uncertainly about the future of sharing.
While many BitTorrent sites and cyberlockers continue to operate as usual, there is a growing group of users who are expanding their horizons to see what other means of sharing are available if the worst case scenario becomes reality.
Anonymous, decentralized and uncensored are the key and most sought-after features. For some this means signing up with a VPN to make their BitTorrent sharing more private, but new clients are also generating interest.
Recent crackdowns have made operators of central file-sharing sites and services more cautious of copyright infringement. Some even went as far as shutting down voluntarily, like BTjunkie.
In the long run this might drive more casual downloaders to legitimate alternatives, if these are available. Those who keep on sharing could move to smaller communities, darknets, and anonymous connections.