Reverse polish notation is really related to
tree traversal algorithms. If you build a
tree whose
nodes are
operations and its
leaves are the
numbers (or
variables), you can express any calculation you like. If you read the
tree in
post order, you get the
reverse polish notation equivalent of that. If you use
pre order or
in order, you get
polish notation and
traditional notation, respectively.
Example:
Building the tree for (3+4)*52 gives us a tree like this one:
()  (2)

(*)  (5)

(+)  (4)

(3)
I know it's an awful way to draw a tree... my excuses...
Inorder traversal gives us 3+4*52
Preorder traversal is  * + 3 4 5 2
Postorder traversal 3 4 + 5 * 2 
Of course, with inorder, you need parenthesis in order to avoid ambiguity, but you don't need them with reverse polish notation.
This was also used in the venerable Forth programming language.