FIDE ID is your individual number (just like a passport or social security number, but for chess). It’s assigned by FIDE once, and is linked to your chess profile. When you take part in official tournaments or on FIDE Online Arena, get titles, and gain your official rating, it’s all linked to your FIDE ID.
You have to have FIDE ID to take part in the official Over-the-board tournaments. You can receive your FIDE ID via a national chess federation or here, on FIDE Online Arena.
FIDE ID issued by Arena is an official FIDE id. You can and should use it both online and otb.
To get FIDE ID on FIDE Online Arena, you need to register and upgrade to PRO. Here is our step-by-step guide on how to do that: