Accessing parent folders

[Randomizer]

A pretty easy question, but I can't find this on the net. How do you access parent folders when using include or fopen and related functions? Basically I want to open parent/child2/file.xxx from parent/child1/script.php or similar (parent/child3/child4/file.xxx from parent/child1/child2/script.php).

Many thanks.

[Weedpacket]

.. means "the parent of this directory".

[Randomizer]

Does this work for multiple levels?

[Weedpacket]

../..
Just like directory paths anywhere else in the civilised world.