vivo y91 factory reset unlock tool

This is the most common meaning. FRP (Factory Reset Protection) helps prevent unauthorized access to a phone after a factory reset. Some tools can bypass FRP on the Vivo Y91 by flashing specific files to the phone's storage.
Warning: Using such tools can be risky and may damage your phone or compromise its security. It's also important to remember that bypassing FRP on a stolen phone is illegal.