GNIS refers to the Geographic Names Information System, an online database that contains information about names and locations of features in the United States and its territories. Some synonyms for GNIS could be location database, place name repository, or geographic feature directory. The system includes more than 2.2 million names of features such as mountains, rivers, and towns, and is updated regularly. It is used by various organizations, including government agencies, academics, and researchers, for mapping, planning, and other purposes. Some related terms to GNIS could be GIS (Geographic Information System), GPS (Global Positioning System), or geolocation technology.