Would need to see the context but I’m guessing a person who only comes out when it’s dark?

“Twilight existence” typically refers to a state of living that’s ambiguous, shadowy, or partially hidden from normal society, similar to life on the edge of visibility or significance. This expression can describe people or groups who are marginalized, those living in semi-legal or isolated conditions, or people in transition, where they exist “between” states. For instance, in literature, characters with a “twilight existence” may lead lives that are incomplete, half-realized, or marked by uncertainty. In sociology or psychology, the term might describe those who feel they don’t fully participate in or connect with mainstream society, such as undocumented workers, the homeless, or individuals isolated by illness or stigma. This phrase draws on “twilight” as the time between day and night, symbolizing something that’s not fully one thing or another. It conveys a sense of liminality—a life or experience hovering between states without fully belonging to any.