Degaussing is the process of decreasing or eliminating a remnant magnetic field. It is possibly named after the Gauss unit of magnetism, which in turn is named after Carl Friedrich Gauss. Due to magnetic hysteresis it is generally not possible to reduce a magnetic field completely to zero, so degaussing typically induces a very small "known" field referred to as bias. Degaussing was originally applied to reduce ships' magnetic signatures during WWII. Degaussing is also used to reduce magnetic fields in CRT monitors and to destroy the data on magnetic media.
Read more about Degaussing: Degaussing Ships' Hulls, Degaussing Monitors, Degaussing Magnetic Data Storage Media