A darkroom is a special room used to make photographs from old-style camera film. It is kept very dark, or lit only with a dim red or orange light, because ordinary white light would ruin the film and the paper. In that room you wash the film in liquids, then shine a controlled light onto paper until the picture slowly appears. This is the real, technical meaning. Though actually, most people today take photos on phones, so a true darkroom is now something you find in art schools, hobby clubs, and with photographers who still love film. People sometimes stretch the word for any room with the lights off, but that is loose talk: a bedroom at night is just a dark room, two words, not a darkroom. When it is written as one word, think of photography.