This file stores information about users.

Each line in /etc/passwd is in this format:

Note: The rpcbind server requires both the user and group daemon, and the tftpd server requires both the user and group nobody

The fields are separated by colons and include:

The user's login name. This can contain any characters except a colon (:), but you should probably avoid any of the shell's special characters. For more information, see Quoting special characters in Using the Command Line.
This field must be empty or x. If empty, the user has no password; if x, the user's hashed password is in /etc/shadow.
The numeric user ID.
The numeric group ID.
A free-form comment field that usually contains at least the user's real name; this field must not contain a colon.
The user's home directory.
The initial command to start after login. The default is /bin/sh.
Note: You can't specify any arguments to the login program.

Here's a sample entry from /etc/passwd:

fred:x:290:120:Fred L. Jones:/home/fred:/bin/sh