Practical Common Lisp

Hi folks,
Had a false start a few months ago with my outdated Lisp-in-a-box on a mac but picked up a cheap as chips Thinkpad and thanks to a very helpul fellow on youTube got emacs,SBCL,Slime installed ok.

Working slowly through the above mentioned book and i'm already stuck on page 23

CL-USER> (defun prompt-read (prompt)
(format *query-io* "~a: " prompt)
(force-output *query-io*)
(read-line *query-io))
;
; caught WARNING:
; undefined variable: *QUERY-IO
;
; compilation unit finished
; Undefined variable:
; *QUERY-IO
; caught 1 WARNING condition
STYLE-WARNING: redefining COMMON-LISP-USER::PROMPT-READ in DEFUN

What does this all mean? it does return PROMPT-READ after all ?

Thanks in advance
milky

*query-io* is global variable. The asterisks are part of the variable name, they are just like any other characters. There is missing one in the last line of source code.