/ = Root directory
. = This location
.. = Up a directory
./ = Current directory
../ = Parent of current directory
../../ = Two directories backwardsAn absolute path refers to the complete details needed to locate a file or folder, starting from the root element and ending with the other subdirectories. Absolute paths are used in websites and operating systems for locating files and folders.
An absolute path is also known as an absolute pathname or full path.
Example:
http://www.foo.com/images/kitten.pngrequire __DIR__ . '/../folder1/folder2/file';path/to/file.php