Even oddly more pedantically, that's the operand stack, not to be confused with the separate return stack. >R and R> move values between the two stacks.
On the other hand, PostScript also has a dictionary stack, which you can use to implement a Smalltalk-like object oriented programming system. And its data types and executable code are basically polymorphic homoiconic JSON (like Lisp), not raw untyped bytes like FORTH.