Surface tracking is the irreversible damage and degradation on the surface of a medium or high voltage cable accessory or insulative material, such as a cable termination, due to the formation of conductive, carbonized paths.
Tracking results when discharges cause carbon to be left on an insulating surface as a result of the degradation caused by the heat of the discharge. This carbon deposit will grow to eventually create a continuous conducting path, which will lead to catastrophic failure.
External Link: https://www.powerandcables.com/3m-terminations-surface-tracking/