used to describe a person who is not heterosexual (= sexually attracted to men if they are a women and women if they are a man) or not cisgender (= having a gender that matches the body they were born with) but keeps that fact secret from other people

The book portrays him as a closeted bisexual.

We want to make it easier for people who might still be closeted, or exploring their gender expression, to feel comfortable enough to talk about it.

used to describe an activity or opinion that someone keeps secret

closeted political dissent 不为人知的政治观点分歧

If someone is closeted somewhere, they stay there, often because they are working hard on something.

She is currently closeted at home working on her new book. 她目前闭门不出，在家写一本新书。