A "seedbox" is a dedicated high speed remote connection, that people use for p2p file transfers. Most common usage is among people who use the bittorrent protocol and feel their home connection is too slow to compete with other users of private sites that judge you based on your download to upload ratio. Using a seedbox allows these users to very quickly download, and therefore upload back data, helping assure a positive ratio. They then generally move the files they want to their home computer via ftp.