In Shakespeare's Macbeth, what is "a tale told by an idiot, full of sound and fury, signifying nothing"?

This line is
taken from act 5, scene 5, towards the end of . At this point, we have
already seen 's murderous rise to power and are already watching the confluence of events that
will bring about his fall.

The fullis spoken after Macbeth learns of the
death of his wife, . To present a portion of the text:

And
all our yesterdays have lighted fools / The way to dusty death. Out, out brief candle! / Life's
but a walking shadow, a poor player / That struts and frets his hour upon the stage / And then
is heard no more: it is a tale / Told by an idiot, full of sound and fury, / Signifying
nothing.(Shakespeare, Macbeth, Act 5, Scene 5)

As can be see from the text, life's essential nature is the subject
of his musings. I'd suggest that, in large part, he is reflecting in the context of wife's
demise. He himself is on the tale end of this entire bloodthirsty road that has brought the both
of them up to this point. Now, as that road is unraveling, Macbeth is finding that life itself
is feeling hollow.