What does get_include_path () mean? What should I do?

What does get_include_path () mean? In this code, set_include_path (INCLUDE_PATH.PATH_SEPARATOR.get_include_path (). What do I mean by include and requ get_include_path?
This code set_include_path (INCLUDE_PATH. PATH_SEPARATOR. get_include_path ());

I can limit the path range of include and require.
However, I echo get_include_path (); the output is F: \ AppServ \ www \ iwb/application/;.; C: \ php5 \ pear
What is next to C: \ php5 \ pear?

------ Solution --------------------
Paer is a PHP library that provides many ready-made encapsulated objects, similar to Javascript JQuery. When you want to use this library, you can put the library file in C: \ php5 \ pear instead of the website directory.
------ Solution --------------------
The get_include_path function returns the current php search path (usually called include_path in php. ini)

When include_path is not set separately, php defaults include_path to.; C: \ php5 \ pear (in window system)