Like JocelynC said, when a chapter is installed on a campus, it is given its own INDIVIDUAL chapter name by their HQ -- instead of #1, #2, #3, etc. they are given Greek names, and most organizations go according to the Greek alphabet. For instance, many of our first ever chapters are called "Alpha", the second one, "Beta" and so forth. Not all chapters are designated this way, however. Pi Beta Phi names their chapters according to their state and order of installation in the state..."Indiana Alpha" for example.

Many other orgs have "Alpha Beta" chapters of their own. JocelynC belongs to the Alpha Beta chapter of Sigma Sigma Sigma. The Alpha Gamma Delta-Alpha Beta chapter is at the University of Michigan. I am an alumna of the Delta Sigma chapter of Alpha Gamma Delta. When you have over a hundred chapters of an inter/national organization, this is the system used to indicate one chapter of this organization.

If and when you do become a new member of a sorority, you'll learn the Greek alphabet and all of this will hopefully make sense.