SFTP (SSH File Transfer Protocol) is a secure file transfer protocol that provides a secure way to transfer files between a client and a server over a network, typically using SSH (Secure Shell) as the underlying protocol. SFTP is different from FTP (File Transfer Protocol) and FTPS (FTP over SSL/TLS) in that it uses SSH for authentication and data encryption, making it highly secure.

Here are the key features and characteristics of SFTP:

1. Security: SFTP utilizes the encryption capabilities of SSH to protect the confidentiality and integrity of data during transmission. All data, including file contents, commands, and authentication credentials, are encrypted, preventing eavesdropping and unauthorized access.

2. Authentication: SFTP uses SSH's authentication methods, such as password authentication and public key authentication, to verify the identity of the client and the server. This ensures that only authorized users can access the SFTP server.

3. Portability: SFTP can run on top of various SSH implementations and can be used on different platforms, including Unix-like systems, Windows, and macOS.

4. File Operations: SFTP supports a range of file operations similar to traditional FTP, such as uploading files to the server, downloading files to the client, renaming files, deleting files, creating directories, and listing directory contents. These operations are carried out securely over the encrypted SSH connection.

5. Directory Navigation: SFTP provides commands to navigate the remote file system, allowing clients to change directories, move between directories, and view file and directory properties.

6. Additional Features: SFTP supports features like resume capability (allowing interrupted transfers to be resumed), file and directory permissions management, and symbolic links.

It's important to note that SFTP is not an extension or add-on of FTP but a completely different protocol that operates over an SSH connection. While FTP and FTPS rely on separate data connections, SFTP uses a single connection for both control and data transfer, making it easier to manage and configure firewalls and network setups.

SFTP is widely used in scenarios where secure file transfer is essential, such as remote server administration, file backups, and secure file sharing. It provides a robust and secure method for transferring files over a network, protecting sensitive data from unauthorized access and interception.