Quickly returning an app to its last good version when a new update causes a problem.
A rollback undoes a deployed update and restores the previous version that worked well. In modern systems it takes one click or command, because every deployed version is kept. The goal is to stop the damage fast, then investigate the cause calmly.
Even with good testing, some problems only appear with real customers. A clear rollback plan turns a mistake from a long crisis into a short blip. But beware: rolling back code does not automatically restore data if the update changed the database.
Practical tip: before any deployment, know how you will roll it back and who is allowed to do it. For updates that change the data schema, take a backup right before and keep the change compatible with the previous version where possible.