Market Is Off

Your roommate wanders into the kitchen without any pants on, singing the opening track to Les Misérables, and starts making an anchovy and praline omelette. You'd probably say, "Huh, Sandy is off today."

Same with the stock market. If the stock market is down on a particular day (the trading equivalent to wandering around without any pants while singing show tunes), traders will say "the market is off today." The term means the major market indices are showing declines. Like Sandy's mental health.