Interoperability means the capability of two or more systems to exchange information and use/interpret the information shared without knowledge of the data structure. According to the online ESRI GIS Dictionary:
The interoperability is required for a GIS user using software from one vendor to study data compiled with GIS software from a different provider.
Spatial data type (for example, GIS, CAD, raster, XML, and LiDAR)
Spatial data format (for example, shapefile, DWG, ECW, GML, and XYZ)