SSH (Secure Shell) is a cryptographic network protocol for secure remote access, command execution, and data transfer over untrusted networks. It provides encrypted communication channels using public-key cryptography, replacing legacy protocols like Telnet and FTP. SSH operates on port 22 by default and is fundamental to modern system administration, DevOps workflows, and secure remote management. The key concept to remember: SSH tunnels all traffic through encrypted channels, meaning not just authentication but also all subsequent data transfer is protected—making it essential for accessing servers, managing infrastructure, and transferring files across networks without exposing sensitive information.