But it isn't important. If you are a reviewer you will have an id number assigned to you. Most people don't know theirs, and it isn't something you ever use. Your handle is what is important. For providers, the id number is important, because it is a way to make sure reviews get applied to the correct person. It can be used in searches, etc.
your ID# will be at the top of the reviews you have written when you go to "My TER" and click on "My Reviews" each review will have your ID#. There is a discussion on this board about this. I can't recall it now but if you do a search you can find it.
Perfectstorm is correct it's not something the guys usually need.