Clarification on terminology as There has been some confusion with EFI and passwords vs. a PIN.

When you set the EFI password, you will be prompted to enter a password. It can be whatever you want and any combo of numbers and letters. This is your EFI password.

Now let's talk about an EFI PIN. As part of iCloud you have Find my Mac. The idea is if someone steals your machine and logs onto the Internet, you could see where the machine is using Find my Mac. One of the features of Find my Mac is you can use it to lock down a stolen device. So if you login to (from another machine) and click on Find my Mac you will see an option to "lock" the stolen Mac. If you click that you will be asked for a four digit PIN. The next time the thief gets on the Internet the stolen machine is going be locked down with that PIN.

So let's say the police find your machine. When you go to use it you will get a screen (below) saying this machine is locked and a prompt for the four digit PIN you entered when you locked the machine. When you enter that PIN, the machine will unlock and you can resume use.

This PIN does reside in EFI, but it is not the same as your EFI password. Two different things for two different purposes.