Peer-to-Peer (P2P) is a data transfer and processing protocol which decentralizes data. Rather than the data being served by a dedicated computer or server bank, it is made available directly from personal computers which are offering it. This protocol can be faster, more efficient, and more reliable if well implemented than the traditional retrieval method from dedicated servers.
Software is required to use Peer-to-Peer transfer. There are paid options, but free software for this purpose also abounds. Some popular programs are BitTorrent, uTorrent (which now shows ads that can be objectionable), and Deluge.
How it works
When a specific piece of data is needed, the torrent program asks what pieces of it other online clients have. It then asks various clients for specific blocks of the download which it does not have. The other clients upload these blocks to that client. Meanwhile, other clients ask what blocks this client has, and may request some. These requested blocks are then uploaded to them.
Trackers are tremendously helpful with traditional Peer-to-Peer sharing. Remote clients may be manually entered and connected to, but if a tracker is used, this server will keep track of who is online, and serve that list to every active client. This enables one to start participating in a torrent, without needing a list of IP addresses.
In more recent years, Peer-to-Peer torrent programs have begun implementing the DHT protocol. This enables the peer cloud to act as its own tracker. This newer function enables the system to run even more efficiently while completely decentralizing the system.
Peer-to-Peer sharing can be a very efficient system. For this reason, some business integrate this into their products. Dropbox is one such company which has started using Peer-to-Peer transfer. This can also be used in an office setting, or by an individual. If for no other reason, one could send an e-mail with a torrent file attached, and the recipient could use that file to download the actual item, which was too large to be attached on its own. However, this is a less efficient use of the protocol. This protocol is also used in the transfer of cryptocurrency like bitcoin and litecoin.
Unfortunately, due to the easy-to-use nature of this, it has taken on a bad name as some people now use it for illegally transferring some files for purposes such as piracy. Since it is decentralized, there is no easy way for law enforcement to stop such transfers.