In ArcGIS world we would be talking about basemap:
A basemap is used for locational reference and provides a framework on
which users overlay or mash up their operational layers, perform
tasks, and visualize geographic information. The basemap serves as a
foundation for all subsequent operations and mapping. Basemaps provide
the context and a framework for working with information
Or in other words:
A map depicting background reference information such as landforms,
roads, landmarks, and political boundaries, onto which other thematic
information is placed. A basemap is used for locational reference and
often includes a geodetic control network as part of its structure.
Or in a nutshell:
The base map is the part of the map I don’t have to make
In contrast, they use term operational information for data that is overlayed on the basemap itself.
WorldAtlas also uses basemap term:
Map on which information may be placed for purposes of comparison or
geographical correlation. The term "base map" was at one time applied
to a class of maps now known as outline maps. It may be applied to
topographic maps, also termed "mother maps" that are used in the
construction of other types of maps by the addition of particular
Together with Wikipedia (although with 'base map' spelling), Garmin GPS manufacturer, matplotlib Python graphing package, data.govt.nz portal and Swiss Federal Statistical Office just to name a few.