TLDR: download this spreadsheet to find out!
"Impostor syndrome (also known as impostor phenomenon (IP) or impostorism) is a psychological occurrence in which an individual doubts their skills, talents, or accomplishments and has a persistent internalized fear of being exposed as a fraud".
Luisa Rodriguez has recently published a great article about it. "We’re obviously not in the business of diagnosing mental health concerns, and we’re big proponents of seeking professional support". However, you can download this spreadsheet to quickly assess the extent to which impostor syndrome experiences interfere with your life, based on the Clance IP Scale.
If any of the Clance IP Scale statements sound like you or someone you know, I would encourage you to read/share Luisa's article.
As Luisa noted here, "A higher score suggests you have more characteristics consistent with imposter syndrome, but note that imposter syndrome might be a useful framing for you even if you only relate to a couple of common experiences".