Server Used in Schools and Workplaces

I am working on setting up a home server using Windows 2003 Server. At my college, I can go to any computer and login using the same credentials. I cannot think of what you would call this system. They also do this in my office. I simply want to know what this system is called so I can research how to set it up on my future home server. Any help would be appreciated.

Thanks in Advance,
Sean

Thanks Rich, that is all I needed to know.
- Sean