What are the grounds on which they allow an annulment? I would think it is considered different than a divorce, as if to say a marriage never happened, or should not have happened due to fraud or something, right?
Discussion
Correct. It is a determination, by a tribunal - diocesan level, but appealable to Rome - that there was never a valid marriage to begin with, due to grave defects like fraud, coercion, impairment, etc.