An unbalanced cable has two wires. A ground and the signal. The audio is the difference between the two. A guitar cable is unbalanced.
A balanced cable has 3 wires. A ground, a signal (+ hot) and a signal with opposite polarity (- cold). The receiver will flip the polarity of the cold signal and add the two signals. The result is that any interference that happens in the cable is also flipped on the cold signal and thereby cancels the interference on the hot signal.
Put in like math: let’s say your audio is 3x and noise is 0.5y An unbalanced cable would deliver 3x + 0.5y =noise being added to the output.
A balanced cable would deliver “hot” 3x + 0.5y and “cold” -3x +0.5y. The receiver flips the cold resulting in 3x+0.5y +3x -0.5y =6x + 0y. This can then be divided by 2 resulting in the correct 3x and no noise.