Definition of "sor"

“The Greeks have tons of influence on campus,” says one student. “Frats and sors allow for smaller groups of friends, making it easier to have a social identity.”

2004, The Unofficial, Unbiased Guide to the 331 Most Interesting Colleges 2005, page 327

If you are not a part of a Frat/Sor, then it seems at though they are non-existent.

2011, Brian Washburn, University of Utah 2012