The curtilage of a listed building is normally considered to be the land, buildings and structures which go with or are ancillary to the principal building. Any buildings or structures which formed part of the land associated with, or belonging to, the principal building at the time of listing are considered to be within the 'curtilage' of the listed building and are therefore considered part of it. Buildings or structures that date from after 1st July 1948, and which are unattached to the listed building, are not considered to be curtilage listed.Typically, structures covered by curtilage listing might include: walls, gates, railings, gatehouses, stables, urns, statues, dairies, barns, privies and cart sheds. To demolish, alter or move any such structure, you will need to apply for Listed Building Consent
This is from Stroud district council's definition , If you google it there are several to pick from, Scotland has it's own definition.