What is the difference between a minor and major nonconformity?

A minor nonconformity is a single or non-critical failure of the ISMS, whereas a major nonconformity is a more systematic or critical failure of a process or key elements of the management system.  If your organisation is attempting to gain third-party certification, a major nonconformity may prevent this certification from being granted.  However, once your organisation has achieved certification a finding of this nature may result in the suspension of your certification in certain circumstances.