A basemap (or base map) is a collection of imported reference data intended to provide visual orientation to users of a map, so that further details can be added and displayed on it in a meaningful way. This may include data on imagery, topography, roads, political boundaries or other things, depending on the purpose of the map.
Waze map editors use the term as a synecdoche for imported roads that have never been edited and for areas that contain them.
Waze basemap in the United States
In many countries, Waze has licensed and imported data on roads and other features from various sources to serve as its basemap, and this is the foundation upon which users and map editors build to create a usable navigation system.