**The Free On-line Dictionary of Computing (30 December 2018):**

postfix notation
postfix syntax
Reverse Polish Notation
reverse polish syntax
RPN
(Or "Reverse Polish Notation", RPN) One of the
possible orderings of functions and operands: in postfix
notation the functions are preceded by all their operands.
For example, what may normally be written as "1+2" becomes "1
2 +". Postfix notation is well suited for stack based
architectures but modern compilers reduced this advantage
considerably.
The best-known language with postfix syntax is FORTH. Some
Hewlett-Packard calculators use it, e.g. HP-25, HP-29C,
HP-41C, HP-23SII.
Compare: infix notation, prefix notation.
(2003-06-23)