Working with Geodatabase Datasets - Learning ArcGIS Geodatabases - page 64

Note that the output is not a feature class but a feature dataset; a group of feature classes.
We will discuss feature datasets in detail in the upcoming chapters.
Note
A feature dataset is a dataset container for other geodatabase datasets. Feature datasets
carry the properties (such as the spatial reference) that all child datasets inherit.
There are three feature classes, Polygon , Polyline , and BelizeBoundary . You
can use the BelizeBoundary feature class and safely delete the other two. To delete a
dataset from a geodatabase, right-click on the dataset and select Delete . You will be