The Full Form of FRP is Factory Reset Protection.

HardReset.info: Android Factory Reset Protection (FRP) is a new feature in some of the devices with Android OS 5.1 or higher. FRP prevents from other people using your smartphone and performing a factory reset without your permission. Factory reset in that case is only possible with access to your Google Account and screen lock information. 

If you perform the hard reset operation on your device with Factory Reset Protection switched on, you have to enter the login and password for the last Google Account that was registered in your cell phone. This security protection will ask for the credentials of old Google Account before the system loads up and you can’t use your device without inputting the appropriate Google details.