Factory Reset Protection (FRP) is a security method that was designed to make sure someone can’t just wipe and factory reset your phone if you’ve lost it or it was stolen. Starting with Android Lollipop, FRP is “standard” in vanilla Android, and most companies making our phones have implemented it in their own models.
Depending on the model of the device, the only way to get access to the device is to have access to the original Google account that was set up on the device. Sometimes a Google account may have 2-factor authentication enabled, meaning the original phone number you assigned to your Google account will receive a security code in order to gain access to the device.