Everyone with an IMDb account has a User ID. The User ID is a label associated with your opinion content if you’ve made that content public. This includes:
Your User ID also appears on Your Activity page. This provides you with a consistent way to be represented across IMDb. You can change your User ID by visiting the Change your User ID page in the Account Settings section.
You can also update the text shown in the description field of Your Activity page. You may decide to do this if you want to share information with others on IMDb, e.g., social media links.
Everyone with an IMDb account also has a private contact name (real name). This appears only in your view, in the navigation bar in the upper right of every IMDb page. Your real name is used for communication with customer service and emails you receive from IMDb.
Your User ID is used internally to identify your contributions to IMDb. Contributions are always anonymous with these exceptions:
If you are an entertainment industry professional with credits listed in IMDb you may have an IMDb name page. This is different than your User ID. See also: What's the difference between an IMDb page and user profile?