An IRCTC User ID is a unique identifier assigned to every user who registers with the IRCTC platform. It is linked to the users mobile number and email address, and is required to successfully book a train ticket on the platform. The IRCTC User ID is also known as the IRCTC Login, and users need to input this ID along with their password to log in to their account and book tickets. If a user forgets their IRCTC User ID, they can recover it by visiting the IRCTC Forgot User ID page on the IRCTC or Goibibo website, and entering their registered email ID or mobile number and date of birth. Alternatively, users can contact IRCTC customer care for assistance. When creating a new IRCTC account, users need to choose a unique username that is between 3 to 35 characters long and contains only letters and numbers.