When you see all uppercase stuff like LIB_PATH, that usually refers to a constant someone has defined like this:
If you try to refer to some constant which hasn't been defined yet -- or just happened to accidentally leave the
$ off a variable you were typing -- then you get the undefined constant error. This commonly happens:
echo FOO; // this causes error
The error in this case is:
PHP Warning: Use of undefined constant FOO - assumed 'FOO' (this will throw an Error in a future version of PHP) in /tmp/foo.php on line 3
This often happens if you forget to
require some file that would initialize your framework or coding environment.