As already mentioned, the debugger tool allows you to examine the state of the execution stack , which is shown in the Backtrace area. This area consists of a sequence of stack frames . A stack frame is a description of some part of a program, or something relating to the program, which is packaged into a block of memory and placed on the stack during program execution. These frames are not directly readable without the aid of the debugger.
There can be frames on the stack representing active function invocations, special variable bindings, restarts, and system-related code. In particular, the execution stack has a call frame for each active function call. That is, it stores information describing calls of functions which have been entered but not yet exited. This includes information such as the arguments with which the functions were called. By default, only call frames for active function calls are displayed in the Backtrace area. See Configuring the debugger tool for details of how to display other types of call frame.
The top of the stack contains the most recently-created frames (and so the innermost calls), and the bottom of the stack contains the oldest frames (and so the outermost calls). You can examine a call frame to find the name of a function, and the names and values of its arguments, and local variables.
LispWorks IDE User Guide (Macintosh version) - 25 Nov 2011