The protocol most commonly used for transferring files over the internet is File Transfer Protocol (FTP). FTP facilitates the transfer of files between a client and a server, allowing users to upload and download files easily. It operates over TCP/IP and can support both anonymous and authenticated access. Variations such as SFTP (SSH File Transfer Protocol) and FTPS (FTP Secure) enhance security by encrypting the transfer process. FTP is widely used for maintaining websites, sharing large datasets, and managing files in cloud environments.