Basemaps - what do we mean?
A basemap is a map layer on which other data can be overlaid and referenced against. It provides orientation and context at a geographical level.
Basemaps are available in many different formats ranging from OS MasterMap Topography data (GML, GeoPackage and Vector Tile formats), to the more dynamic Web Map Tile Services (WMTS) such as the OS Maps API.
When considering what source or type to use it is prudent to first ask your software supplier what basemap data / mechanism they are able to support.