This variable is used by the debugger when it displays the stack frames. Open frames are made by the system and are normally not shown by the debugger. However if
*print-open-frames* is set to
t then the open frames are displayed. It is unlikely that you need to examine open frames: their use is connected with implementation details.
USER 52 > (setq dbg:*print-open-frames* t)
Type :c followed by a number to proceed
LispWorks User Guide and Reference Manual - 20 Sep 2017