Signal and noise
Electronics and telecommunications engineers distinguish between the signal that is being communicated between two locations and the random noise that is added by the communications channel. The noise degrades the signal and, in the worst cases, can make the signal difficult to detect.
Audio equipment often quotes its signal-to-noise ratio as a measure of quality. Noise again deteriorates the signal — the 'perfect' music that you want to hear.
Signal = information you want
Noise = 'random' modification to the signal
Example of signal and noise
The word 'CAST' can be seen below. This is the signal in the picture.
Drag the slider to the right to add random noise to the picture. Even when the slider is in the middle, it is becoming hard to distinguish the signal in the picture.
Adding noise makes it harder to detect the signal in the picture.
The concepts of signal and noise also apply to data sets.