TTY originally meant a teletype terminal, but in modern Unix-like systems it usually refers to a text terminal session or the controlling terminal attached to a process. The system may expose this through devices such as /dev/tty or through pseudo-terminals (PTYs) created by terminal emulators and remote shells. In practice, a TTY is what gives a command-line program interactive input, output, job control, and line discipline.
TTYs matter in cyber security because they affect how operators and attackers interact with a system. Many remote access tools begin as a simple shell and are later upgraded to a TTY so commands behave normally, history works, and full-screen tools can run. Defenders also care about TTY context when auditing sessions, enforcing sudo policies, or spotting suspicious interactive logins. Understanding TTYs helps explain why some shells feel limited, why others feel fully interactive, and how text-based access can be monitored or hardened.