Source: All The Bright Places by Jennifer Niven, page 284.

Context: “I want to get away from the stigma they all clearly feel just because they have an illness of the mind as opposed to, say, an illness of the lungs or blood.”

In their words: “a mental or physical mark that is characteristic of a defect or disease:” – https://www.dictionary.com/browse/stigma?s=t

In my words: a mental or physical imperfection.