Some phones will use Android's Factory Reset Protection (FRP) and some will have a privacy password baked into the hardware. Some will have both. In either case, they are designed to prevent unauthorized people from resetting your phone and being able to use it.
If you reset your phone without removing the default accounts, or purchased a second hand phone where the seller neglected to do that, you will need the Google account password last used for the device. If you don't know that, you're kind of out of luck. There's no way to bypass that short of sending it back to the manufacturer to reflash the firmware.
If it's a manufacturer's security password, it would help to know the make and model of the phone, not just your carrier in order to point you in the right direction.