Stdin
From Hackepedia
stdin is short for standard input. It is always descriptor number 0 in a unix program. In OpenBSD stdin can be represented as /dev/fd/0 or /dev/stdin. You can see more about this by typing "man 4 stdin" or "man 4 fd". Standard input is defined in /usr/include/unistd.h as a macro that is called STDIN_FILENO and its value is 0.
