n. (Electronics, Information science, Experimental science) The ratio of the intensity of a signal{ 2 } to the background noise detected by a measuring instrument, especially in a communications channel; the higher the ratio, the more accurately the information contained can be interpreted. The term is applied not only to human communications, but to the detection of information in any system that is being studied to gain knowledge; as, the signal-to-noise ratio of light signals in older optic fibers drops to an unusable level after several miles.. [ PJC ]