What is an FTP server?
The standard Internet protocol which is used for conveying files between computers on the Internet over TCP/IP connections is called the File Transfer Protocol (FTP).
FTP sessions work in active and passive modes. In active mode, after a client initiates a session via a command channel request, the server initiates a data connection back to the client and begins transferring data; while in passive mode, the server uses the command channel to send the client the information it needs to open a data channel. Passive mode works well across firewalls and Network Address Translation (NAT) gateways since it has the client initiating all connections.
Basically, FTP is a client-server protocol that relies on two communication channels between a client and a server - a data channel for transmitting file content and a command channel for controlling the interaction. Clients initiate interactions with servers by requesting to download a file; using FTP, a client can either upload, download, delete, rename, and move and copy files on a server.
A user typically needs to log onto the FTP server. Anonymous FTP is a name for servers which hold all of their content available without login.