To degauss is to demagnetize or to remove the magnetic field from an object.
Among other duties, Ensign Sito Jaxa had to degauss the main deflector dish while filling in at ops on board the USS Enterprise-D in 2370. (TNG: "Lower Decks")
While investigating the nucleogenic cloud being for omicron particles, nucleogenic particles stuck to the hull of the USS Voyager, forcing repair crews to degauss the hull. (VOY: "The Cloud")
A magneton scanner has the ability to degauss a transporter room in approximately five minutes. (VOY: "Learning Curve")