What protocol is commonly used for file transfer between hosts on the internet?

The File Transfer Protocol (FTP) is a widely used protocol designed specifically for transferring files between hosts on the internet. It facilitates the upload and download of files, allowing users to connect to another server or computer over a network to transfer data. FTP operates over the Transmission Control Protocol (TCP), ensuring reliable communication and data integrity throughout the transfer process.

While other protocols listed also serve important functions in internet communication, they are not primarily designed for general file transfer tasks. Hypertext Transfer Protocol (HTTP) is used mainly for transferring web pages and associated resources, Secure Copy Protocol (SCP) is focused on securely transferring files between hosts using SSH (Secure Shell), and Simple Mail Transfer Protocol (SMTP) is specifically intended for sending emails. Each of these serves its distinct purpose, while FTP stands out as the foundational protocol specifically tailored for file transfers, making it the most appropriate answer in this context.