An annotation can be understood as an attribute or property containing information associated with some element of a Modelica model. Examples are model documentation and graphical layout information concerning icons and connections associated with models. The graphical view usually makes models easier to understand.
Resistor1 is an example of an annotation containing information about the graphical layout of an icon representing a resistor model, the annotation has the name Icon and contains instances of the graphical annotation elements Rectangle, Text, Line, etc.