iPhone recovery refers to the collective measures and processes used to restore an iPhone to normal working condition. It is done whenever any problem causes an iPhone to not respond, behave unexpectedly or become inaccessible.
Techopedia explains iPhone Recovery
iPhones generally crash or become unresponsive after installing new updates or when a malicious virus corrupts, deletes or overwrites critical system/iOS files.
Typically, iPhone recovery requires the user to connect the iPhone to a computer with iTunes installed and a valid account on iTunes. More importantly, it requires that the user has created an iPhone backup onto a computer or iCloud.
Once connected, the user can select and restore the iPhone from available backups.
Recovery problems that are due to hardware defects must be manually corrected by repairing or replacing faulty parts.