InterpretationBox[boxes, expr] displays as boxes but is interpreted on input as expr.
InterpretationBox provides a way to store hidden information in Mathematica output.
InterpretationBox is generated sometimes in StandardForm output, and often in TraditionalForm output.
The following options can be given:
If you modify the displayed form of InterpretationBox[boxes, expr] only boxes will be modified, and there is no guarantee that correct correspondence with expr will be maintained.
InterpretationBox has attribute HoldComplete.
See The Mathematica Book: Section 2.8.10.
See also: TagBox, FormBox, ToExpression, ButtonBox.