Standard VII: CFA Responsibilities. Members and Candidates must not engage in any conduct that compromises the reputation or integrity of CFA Institute or the CFA designation, or the integrity, validity or security of the CFA examinations. This Standard specifically addresses the integrity or validity of the CFA examination process.
Incidental means secondary in time or importance. If you lose weight because you moved and must walk further to school, the weight loss was incidental to the move. When something is incidental, it is never the main thing. It's okay to include incidental details as they can add depth to your storytelling, but they are never crucial to the story.
A good but fairly general definition of an incident is the act of violating an explicit or implied security policy. Unfortunately, this definition relies on the existence of a security policy that, while generally understood, varies among organizations.