What is the definition of Narcissism?

You can look in the DSM for a detailed clinical definition. But fundamentally it's a sense of entitlement. They feel entitled to special treatment due to their stunning beauty and/or stable genius. They are better than everyone else and are thus entitled to be treated in a way fitting of their stature.

The definition=My Mother!

https://en.m.wikipedia.org/wiki/Narcissism

If you are wondering about it, I'm sure you're not being treated well by someone. For me, the most challenging part of living with a narcissist is that most days they make me question my own sanity.
Click that blue shape that says narcissism under your question.
https://www.agingcare.com/topics/209/narcissism

Here is a great article that explains narcissism by a therapist, with links to even more information.

https://www.forbes.com/sites/kathycaprino/2016/07/09/how-being-raised-by-a-narcissist-damages-your-life-and-self-esteem/#752f0ca82c67