Kazaa Media Desktop (once stylized as "KaZaA", but later usually written "Kazaa") was a peer-to-peer file sharing application using the FastTrack protocol licensed by Joltid Ltd. and operated as Kazaa by Sharman Networks. Kazaa was subsequently under license as a legal music subscription service by Atrinsic, Inc., which lasted until August 2012. According to one of its creators, Jaan Tallinn, Kazaa is pronounced "ka-ZAH" ().

Kazaa Media Desktop was commonly used to exchange MP3 music files and other file types, such as videos, applications, and documents over the Internet. The Kazaa Media Desktop client could be downloaded free of charge; however, it was bundled with adware and for a period there were "No spyware" warnings found on Kazaa's website. During the years of Kazaa's operation, Sharman Networks and its business partners and associates were the target of copyright-related lawsuits, related to the content distributed via Kazaa Media Desktop on the FastTrack protocol.

By August 2012, the Kazaa website was no longer active.