Like late-night commuter trains

• Time of few users
• Not the busiest
• At a time when demand is less
• Reduced-price, most likely
• Outside of rush hour
• Not rush hour
• Non-rush-hour, say
• Not at the time of highest demand
• Going to arouse, picked up when it's not so busy

Wiktionary Word definitions in Wiktionary
a. (alternative form of off-peak English)