Each word takes a fixed number of arguments and has a fixed number of return values. Arguments to words are passed on a data stack, using reverse Polish notation. The stack is used just to organize calls to words, and not as a datastructure. The stack in Factor is used in a similar way to the stack in Forth; for this, they are both considered stack languages. For example, below is a snippet of code that prints out "hello world" to the current output stream: