The movement of a device (visual, ultrasonic, etc.) over a wide area as opposed to a spot reading and used to find flaws/defects (e.g. the thinnest thickness measurement at a CML or cracking in a weldment). See guidance contained in API 574.
Source: API 570, Piping Inspection Code: In-service Inspection, Rating, Repair, and Alteration of Piping Systems, Fourth Edition, February 2016, with Addendum May 2017. Global Standards