"Dim" was a 21st century slang term for inhabitants of the United States of America' Sanctuary Districts. "Dims" were usually people with mental health problems. Grady was classed as a dim in the 2020s.
In 2024, while Benjamin Sisko and Julian Bashir were stranded in the past, they were processed into the San Francisco Sanctuary District by Lee who noted that though their paperwork labeled them as dims they didn't strike her as such. (DS9: "Past Tense, Part I", "Past Tense, Part II")