maintenance window
also: scheduled downtime, maintenance period, planned downtime
A scheduled period when a system is taken offline or services are interrupted for updates, patches, or repairs. During this time, users typically cannot access the system or services.
A maintenance window is a planned downtime period announced in advance to users and administrators. It allows teams to perform critical operations like applying security patches, upgrading software, replacing hardware, or performing database maintenance without disrupting active users.
Maintenance windows are typically scheduled during off-peak hours—evenings, weekends, or holidays when fewer users depend on the system. For example, a web hosting company might announce: "System maintenance scheduled Sunday 2–4 AM UTC; services will be unavailable during this period."
Good practice includes: sending advance notifications (48–72 hours), choosing low-traffic times, documenting planned changes, testing updates beforehand, and having a rollback plan if something fails. This minimizes user impact while ensuring systems stay secure and stable.