Definitions for "off-peak"
Having less than maximal use or demand or activity; -- of a period of time occurring as a defined part of a time cycle; as, off-peak telepone rates are available at night and on weekends; off-peak fares.
This is the time of the day, not during business hours (typically 7:00 pm to 7:00 am), when telephone rates are lower than during high-traffic, on-peak times (during business hours).
Generally, the hours from 11:00PM to 6:00AM, when demand for electricity is low.
A time of year when business is traditionally slow for the travel industry.