Materiality is defined in ISA 320 to be the expression of the relative significance or importance of a particular matter in the context of the financial statements as a whole. A matter is material if its omission or misstatement would reasonably influence the decisions of an addressee of the auditors report. Materiality is not capable of general mathematical definition as it has both quantitative and qualitative aspects.
The auditors‘ responsibility is to plan and perform their audit to obtain reasonable assurance that the financial statements are free of material misstatement and give a true and fair view. Thus anything that would distort the view given by accounts must lead to a qualification, but only if it is material.