A feature is the spatial description of a real-world entity such as a road, a utility pole, or a river. Features are stored in a spatial database or file. The spatial database or file is referred to as a feature source .
To access data through FDO
If this feature source contains only a single feature class, that feature class is selected automatically. If it contains multiple feature classes, you can right-click any of them and select Select All or Select None.
To bring in a subset of the data, click the down arrow and select Add To Map With Query. See To Filter Features When You Add Them to a Map.