To not know something that other people do. Somehow, everyone knew that Alicia had quit school except for me—I was totally in the dark.No, I don't know who's going to get the promotion—now that I'm off the executive board, I'm in the dark about a lot of things.
to not know about something that other people know about I'm totally in the dark. I don't know what's going on. (often + about ) We're still in the dark about whether any jobs are going to be cut.