1. In general, the change produced in the output of a device per unit change in the input.
2. The magnitude of the change in the indicated value or deflection of a measuring instrument produced by a specified change in the measured quantity. It is usually quoted as the magnitude of the measured quantity required to produce full-scale deflection.
3. The ability of a radio receiver to respond to weak input signals. It is the minimum signal input to the receiver that produces a particular output value under stated conditions, particularly a designated signal-to-noise ratio.