Errorlevel is a return code sent by a terminating program such as batch,
exe, com or any applications. Errorlevels are not a standard feature of
every command. What the return code means is up to the programmers thought.
However, most programmers agree that an errorlevel 0 means the command
executed successfully, and an errorlevel 1 or higher usually spells trouble.
But there may be some exceptions to this general rule.