A Facebook user ID is a unique identifier given to each person who uses Facebook. A user's Facebook user ID consists of their name and a string of numbers and letters and if you want to check anyone's ID you can check with Facebook's ID finder by putting anyone's User Profile URLs into the tool and also you can check bulk Facebook ID numbers:
A Facebook user ID is a unique identifier assigned to each person who uses Facebook. A Facebook user ID is not a real name; rather, it's just a number. You may have seen your own Facebook user ID before if you've ever logged into Facebook using your email address instead of your actual name.