Bootloader unlocking is the process of disabling the bootloader security that makes secure boot possible. It can make advanced customizations possible, such as installing custom firmware. On smartphones, this can be a custom Android distribution or another mobile operating system. Some bootloaders are not locked at all and some are locked, but can be unlocked with a command or with assistance from the manufacturer. Some do not include an unlocking method and can only be unlocked through a software exploit.
Bootloader unlocking is also done for mobile forensics purposes, to extract digital evidence from mobile devices, using tools such as Cellebrite UFED.