As in signal to noise. In communication theory, signal is meaningful information. Noise is not. Unless we sit quietly in a dark cave all day, we are bombarded with signals and noise. The human brain has evolved to be able to separate the two, eat or be eaten. In the modern world, the increase of abstract and artificial signals has exploded to the point where almost all of what we process is now noise. There are ways to deal with this. Meditation and other mental disciplines can create a haven where the self can focus on "the signal".
Curiously, many people enjoy the noise, and embrace it. When the signals one perceives as important are negative or intolerable, the temptation to escape them, through drink or drugs is almost irresistible. The noise blocks out the signal (if only for a while) but at a cost. Intolerance and hatred can supply a signal, if the recipient focuses only on that message, any other information becomes noise and is ignored.