EA allows you to relate elements together using connectors - the lines which appear on diagrams. One of the great things about EA is that it allows you to link elements using all kinds of connector types, all of which can be printed with eaDocX.
But there are some ways in which EA Elements can be linked which DON'T use connectors. One of those is the Instance Classifier.
The most obvious usage of this is to show which Instances relate to which classes. So, you might create a Class diagram:
..then create some instances of those classes, on an EA Object Diagram:
These are some instances of Class1 and Class2, added to the diagram by dragging/dropping 'Class1' or 'Class2' onto the diagram, and telling EA to make them 'Instances'.
In the EA database, these Instances 'know' which class they are instances of, because EA remember that in the 'Instance Classifier' is each instance.