The mv command is used primarily to move files and directories from one location to another or to rename them. It's an essential command for managing the filesystem structure. It does not actually copy the file content to a new location but rather changes the file's index node (inode) information in the filesystem's table to reflect the new location or name. This is why the correct answer is 'Moving and renaming files and directories', as it accurately describes the action performed by the mv command. The options 'Copying files to a new directory' and 'Creating a duplicate of a file' suggest replicating the file's content, which is not the behavior of mv; for those purposes, the cp command would be used. Lastly, 'Changing file permissions' is an operation performed by the chmod command, not mv.