This comes up if you're using the Slime interface to run Clozure CL under Emacs, and you are doing Cocoa programming which involves printing to *standard-output*. It seems as though the output goes nowhere; no error is reported, but it doesn't appear in the *slime-repl* buffer.

For the most part, this is only relevant when you are trying to insert debug code into your event handlers. The SLIME listener runs in a thread where the standard stream variables (like *STANDARD-OUTPUT* and and *TERMINAL-IO* are bound to the stream used to communicate with Emacs; the Cocoa event thread has its own bindings of these standard stream variables, and output to these streams goes to the *inferior-lisp* buffer instead. Look for it there.