adv. or adj. phr. , informal In an unprofitable way; so as to lose money. A large number of American radio stations operate in the red. A rich man who has a farm or ranch often runs it in the red, but makes his money with his factory or business.
Antonym: IN THE BLACK. (From the fact that people who keep business records usually write in red ink how much money they lose and in black ink how much money they gain.)