"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."
This line means that life is ultimately meaningless. The "sound and fury" refers to the noise and commotion of human existence, the struggles, passions, and emotions that we experience. But Macbeth suggests that these things ultimately signify nothing, because we all die and are forgotten.
So, "sound and fury" does not signify something on its own. It's a metaphor for the chaos and drama of life, which Macbeth believes is ultimately pointless.
However, the phrase can be interpreted in different ways. Some people argue that "sound and fury" *does* signify something, namely the inherent tragedy and beauty of human life. Others might see it as a reminder that we should focus on living meaningful lives despite the inevitability of death.
Ultimately, the meaning of "sound and fury" is open to interpretation, just like the meaning of life itself.