(bī’ ∂s) 1. The amount by which the average of a set of values departs from a reference value. 2. Superposing an additional magnetic field upon the magnetic field associated with the signal during magnetic tape recording. Used to obtain a linear relationship between the amplitude of the signal and the remanent flux density in the recording medium. See ac-bias recording. 3. A voltage that is maintained at a point in a circuit so that the device will operate with desired characteristics. 4. A diode is said to have forward-bias when the voltage across it is such that current flows through it, and back-bias when the opposite polarity is maintained so that no current flows.