Audit findings and definitions

Answer:
When an auditor performs an audit, he or she compares the reality with the audit criteria. If the reality is not according to the audit criteria, we have a Non-Conformity. If the reality is according to the audit criteria, we have a Conformity.
Even when the auditor identifies a Conformity he or she can also find, due to his experience, an Opportunity for Improvement. Some auditors also use word Observation.
Based on ISO 19011:2018 one can say that:
Non-Conformity – it is when an audit criteria, a requirement is not fulfilled
Conformity - it is when an audit criteria, a requirement is fulfilled

ISO 19011:2018 and ISO 9000:2015 do not have definitions either for Opportunity for Improvement or for Observations. Nevertheless ISO 19011:2018 states that the findings of an audit can lead to opportunities for improvement but onl y defines improvement. An activity to improve performance.
So, the evidence presented indicates that a requirement has been effectively implemented, but based on auditor experience and knowledge, the organization can take advantage of modifying its approach.

You can find more information about audits:
- Article - How to write a good ISO 9001 audit nonconformity? - https://advisera.com/9001academy/blog/2018/04/24/how-to-write-a-good-iso-9001-audit-nonconformity/
- [free course] ISO 9001:2015 Internal Auditor Course - https://advisera.com/training/iso-9001-internal-auditor-course/
- book - ISO Internal Audit: A Plain English Guide - https://advisera.com/books/iso-internal-audit-plain-english-guide/