Coin Grading

Superb, used in coin descriptions, is a grade modifier used to indicate a particularly nice coin for the grade.  Superb usually indicates a very attractive coin for the grade.  What makes a coin "superb" is mostly subjective and the opinion of the grader.   

Antiquities Grading

A completely intact piece with original surfaces and glaze or patina.  None but the most minute chipping or corrosion.  A museum quality piece.  When a fragment is offered, the grading is for jus that portion present.