'Scheduling' is shorthand for the process through which nationally important sites and monuments are given legal protection by being placed on a list, or 'schedule'. English Heritage takes the lead in identifying sites in England which should be placed on the schedule by the Secretary of State for Culture, Media and Sport.
A schedule has been kept since 1882 of monuments considered to be of national importance by the government. The current legislation, the Ancient Monuments and Archaeological Areas Act 1979, supports a formal system of Scheduled Monument Consent for any work to a designated monument.
Scheduling is the only legal protection specifically for archaeological sites.
'Scheduled Monuments: An English Heritage Guide for Owners and Occupiers'. English Heritage, 2009. You can download this guide here as a PDF document.