The Backtrace tab displays the function calls on the execution stack in the code being stepped.
The topmost item in the backtrace area shows the next step, known as the status. When calling a function, the status item is represented by a 
icon and contains the arguments represented as subnodes with a yellow disc 
icon. When returning from any form, the status item is represented by a 
icon and contains the return values. When evaluating a form, the status item is represented by a 
icon. You can see the contents of the status item by expanding it. You can make the status item expand automatically if you wish, as described in Backtrace preferences.
The second topmost item in the backtrace area is the active frame represented by a 
icon. This shows the function executing when the breakpoint was reached, and its arguments which are represented as subnodes with a yellow disc 
icon.
Other call frames on the stack are represented in the same way, below.
A subnode with a cyan disc 
icon represents some other frame.
For function calls, arguments and local variables can be seen by expanding the item. You can make the active frame expand automatically if you wish, as described in Backtrace preferences. Just as in the Backtrace area of the Debugger tool, these stack frames and variables can be operated on using the Frame and Variables menus. For details, see Backtrace area.
Double-click on a status or call frame node to show the source of that function, if available, in the Editor. Double-click on the disc icons to show that variable in the Inspector.
LispWorks IDE User Guide (Unix version) - 25 Nov 2011