"Beginning in the fall of 2012, Princeton University will prohibit freshmen from affiliating with a fraternity or sorority or engaging in any form of "rush" at any time during the freshman year.
The decision to institute the ban is being communicated this week to all returning Princeton undergraduates by President Shirley M. Tilghman, who made the decision based on recommendations from a student-faculty-staff working group on campus social and residential life that submitted its report last spring. The decision is being communicated to all entering freshmen and their families by Vice President for Campus Life Cynthia Cherrey and Dean of Undergraduate Students Kathleen Deignan.
The name "rush" comes from the unraveling of fraternity and sorority recruiting, which became earlier and earlier over time. Here's an old paper on the subject:
Mongell, S. and Roth, A.E., "Sorority Rush as a Two-Sided Matching Mechanism," American Economic Review, vol. 81, June 1991, 441-464