factory reset

A factory reset, also known as hard reset or master reset, is a software restore of an electronic device to its original system state by erasing all data, settings, and applications that were previously stored on the device. This is often done to fix an issue with a device, but it could also be done to restore the device to its original settings.
Since a factory reset entails deleting all information stored in the device, it is essentially the same concept as reformatting a hard drive. Pre-installed applications and data on the card's storage card (such as a microSD card) will not be erased.
Factory resets can fix many chronic performance issues (such as freezing), but it does not remove the device's operating system. Factory resets can also be used to prepare a device for sale, refurbishment, disposal, recycling, donation, or other transfers of ownership by removing personal data and settings associated with the previous owner.

View More On Wikipedia.org