satellite
A detached part of a structure which nevertheless belongs to that structure as an integral part.
A satellite is a section of a structure which is physically detached from it, or which appears separately at ground level when connected underground. Only certain types of structures allow satellites, including castles, fountains, monuments, and sculptures. Regular buildings and most other construction types are considered distinct from any physically detached structures.
The part retains an integral relationship to the larger object despite physical separation at ground level. An underground connection can coexist with that separate surface appearance.
The stated allowance is limited to particular structural forms. An ordinary detached building generally has its own identity rather than becoming a satellite of another building.