Imposter Syndrome
The idea (and fear) that one will be exposed as a 'fraud' in their position or for their accomplishments, even in the face of objective evidence to the contrary.
Origin
Clinical psychologists Pauline Rose Clance and Suzanne Imes first described what they called the "impostor phenomenon" in a 1978 paper in Psychotherapy: Theory, Research & Practice, based on observations of over 150 high-achieving women. Originally theorized as primarily affecting women, subsequent research found the experience widespread across genders, and popular usage shifted the name from "phenomenon" to "syndrome."
Everyday Use
This can be a daily encounter for so many of us. What I find particularly helpful to remember about Imposter Syndrome is that it isn't just something that we experience ourselves but that everyone else can be experiencing simultaneously. We sometimes get so wrapped up in being called out for not belonging, that we don't realize the entire room feels that way too, and it gives way to insecurity, fear, even lashing out in unexpected and unhelpful ways. We are all on a journey of belonging.