A geodatabase is a central storage location for features, related datasets and behaviors. GDBs are the standard GIS storage model of choice over the previous ESRI storage formats, the coverage and the shapefile.
The geodatabase has 2 major concepts
It is a relational database offers a seamless physical storage location that makes it easy to scale GIS datasets to extremely large sizes and numbers of users. Tables provide the primary storage mechanism for geographic datasets, query and processing.
Geodatabase elements are object-oriented and can extend simple tables, features, and rasters to add rich behavior, data integrity, and data management capabilities. The geodatabase schema includes the definitions, integrity rules, and behavior for each of these extended capabilities. These include properties for coordinate systems, coordinate resolution, feature classes, topologies, networks, raster catalogs, relationships, domains, and more.