What is Signal to Noise Ratio?

The signal to noise ratio, often abbreviated S/N, is exactly what it sounds like; it’s the ratio of the magnitude of the signal to the magnitude of the noise. Experiments need a large S/N to be able to distinguish features in the signal from the noise. If the S/N is too small, the signal gets lost in the noise and quantities like peak wavelength and peak width become harder to estimate with any certainty.