Binance ID or UID is a unique identifier allocated to each account. You need to provide your User ID for customer support issues. Follow the below steps to find it on the Binance website or App.
On Binance website:
Log in to your account and go to [Profile] - [Dashboard]. You'll see your User ID next to your email address at the top of the page.
On Binance App:
Tap the [Profile] icon on the top left corner. You will then see your user ID under your email address.