Signal-to-Noise Ratio
A measure used in science and engineering that compares the level of a desired signal to the level of background noise.
Origin
The concept emerged from electrical engineering research at Bell Laboratories in the 1920s: John B. Johnson identified thermal noise in electronic circuits in 1927, and Harry Nyquist provided the thermodynamic explanation in 1928. The formal ratio — signal power divided by noise power — became a standard measure of communication system quality. Claude Shannon embedded it at the heart of information theory in his landmark 1948 paper, showing that channel capacity is a direct function of the signal-to-noise ratio. The phrase migrated from engineering into everyday language through the late 20th century as a metaphor for meaningful content versus interference.