Object type is used to classify objects. Technically an Object Type is a class, and objects are its instances.

If you are used to RDBMS concepts, an Object Type is a table. It is possible to specify the attributes of an Object Type by editing the attribute types.

While adding an Object Type it is possible to specify if it is a sub-class of another Object Type.
Some times, you may want to make an Object Type an instance of another class (MetaType). Just be warned that MetaType doesn't mean super-class.