Your UTORid (along with your password) is your userid for a number of different services. Some of these are:

An increasing number of websites are using Weblogin to give users the experience of single sign-on. You log in (authenticate) once using your UTORid and password and you can access participating websites without having to authenticate again. For more information, please see weblogin.

There are other services.  Not everyone is eligible for every service.

How do I get a UTORid?