The sharing of files and materials between people connected through the internet.
P2P stands for peer to peer. This type of networking is most readily associated with file sharing services in the music and video sector that allow downloads of content to take place without needing a single central repository of data. There are many types of peer to peer communication tools such as instant messenger and chat software that allow text conversations to be shared in real time with many participants. Similarly the migration of voice telephony to the internet (VoIP) unlocked more ways of harnessing peer to peer activity.
P2P was made famous by BitTorrent, a technology and client for sharing files (bundled as torrents which uniquely identify the files) through the internet in a de-centralised fashion.