passwd(5) - Unix First Edition Manual Page
11/3/71PASSWD (V)

NAME passwd -- password file
DESCRIPTION passwd contains for each user the following information:

name (login name)password numerical user IDdefault working directory program to use as Shell This is an ASCII file. Each field within each a user'sentry is separated from the next by a colon. Each user is separated from the next by a new--line. If the passwordfield is null, no password is demanded; if the Shell field is null, the Shell itself is used.

This file, naturally, is inaccessible to anyone but thesuper--user.

This file resides in directory /etc.
SEE_ALSO /etc/init
OWNER super--user