"Material adverse change": MAC). A clause in a loan agreement. Normally it is intended as a 'catch-all' clause and states that if in the opinion of the lender there is a change in the circumstances of the borrower that is both material and adverse, then this will constitute an event of default. Not surprisingly this is a contentious clause, depending on who determines 'material', and how. Modified forms of the clause may require the opinion to be 'reasonable' or replace the 'opinion' with an objective test.