In magnetic recording technology (disk and tape), the presence among the signals read from the device of one or more bits that had not been deliberately written there. This is the result of a fault condition, often imperfect erasure of data previously on the medium, and will generally be a problem only in interrecord gaps (elsewhere it will be dealt with by the same means provided for drop-out): magnetic tape and disk systems normally have means of identifying and coping with this problem.