debugger-args is a variable defined in `debug.el'.
Its value is

Arguments with which the debugger was called.
It is a list expected to take the form (CAUSE . REST)
where CAUSE can be:
- debug: called for entry to a flagged function.
- t: called because of debug-on-next-call.
- lambda: same thing but via `funcall'.
- exit: called because of exit of a flagged function.
- error: called because of `debug-on-error'.