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
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.
https://www.forbes.com/sites/kathycaprino/2016/07/09/how-being-raised-by-a-narcissist-damages-your-life-and-self-esteem/#752f0ca82c67
Click that blue shape that says narcissism under your question.
https://www.agingcare.com/topics/209/narcissism