Presents is a USC tradition that occurs on Parent's Weekend. On Saturday, all the sororities hold a Presents party where the new members of the chapter are introduced or "presented" to the rest of the campus. The new members wear white dresses (think Debutante style) and the houses are all decorated. I think UCLA has a similar tradition, although theirs seems a bit more low-key.
We had the same tradition at San Diego State when I was a collegian a zillion and one years ago.
A New Member Walking Through the Presentation Arch
Each chapter at SC has different customs for Presents. The Tri Deltas walk through a Presentation Arch. Pi Phis are "crowned" with a circle of flowers. Delta Gammas walk down a curved staircase carrying a bouquet. After presentations receptions or brunches are held in the chapter houses which are decorated with sorority symbols and many vases of fall blooms.