P2P = Peer to Peer.

Networks where every user on the network shares their music files with every other. And internet version of a swapmeet.

Some networks cost dosh to join and stay in and pay the Performings Rights Society some royalties, others are "free" by which is meant two things - either the softwear comes with lots of spy and ad-ware, or the artists and companies are being ripped off (alas sometimes both too). With Broadband these days even entire TV series, and movies, get downloaded.