A word thrown around too often nowadays and minimizes the severity of true narcissism. It's not a game, or just a self centered person simply being an a-hole.
It's a result of the natural process of individuation going awry. A child goes through a stage of natural narcissism as a toddler. The cognitive separation from mother around 18 months goes through the natural stages of external objectification and grandiosity. If these stages are not completed successfully (itself a result of abuse/toxicity) it results in the high probability of narcissism in adulthood.
A true narcissist is a predator and often not found out until their victim is already ensnared in their psychological abuse. The abuse legitimately affects the way your brain processes reality. It's sick and a horrible thing to experience. I'm still recovering and trying to move beyond the trauma bonding from loving a narcissist.
There are narcissists here on SW. Most will never see it unless entangled with them. Please be careful.