ED2K (eDonkey2000) is a peer-to-peer file sharing protocol that was widely used in the early 2000s. It allows users to share files with each other directly, without the need for a centralized server. ED2K was popularized by the eDonkey2000 client, which was one of the first peer-to-peer file sharing programs.

qBittorrent is a popular open-source BitTorrent client that allows users to download and share files over the internet. One of the key features of qBittorrent is its support for various torrent protocols, including ED2K.

qBittorrent supports ED2K through its built-in ED2K hash parser, which allows users to download files from ED2K servers. When a user adds an ED2K link to qBittorrent, the client uses the ED2K hash to locate the file on the network and begin downloading it.