The listener is another name for the read-eval-print loop (REPL) which allows you to interactively evaluate Lisp forms and see their output and return values. Lisp programmers typically do incremental development and testing in a listener before saving the working code to disk.
This chapter describes the basic use of a LispWorks listener. You might access this in a terminal (Unix shell) or MS-DOS command window. Alternatively the LispWorks IDE contains a graphical Listener tool which runs a REPL and supports all the functionality described in this chapter, as well as its own graphical features. Please refer to the LispWorks IDE User Guide for details specific to the graphical Listener tool.
LispWorks User Guide and Reference Manual - 13 Feb 2015