Phi Gamma Pi:
On the night of pledge initiation Phi Gamma Pi gives their new members an "Emerald Buddy." That girl gives the new member a decorated pledge binder with their new member class on the cover of it. This person is from the pledge class before. As everyone has said, that person is their temporary or pseudo Big.

A week or 2 before initiation week the new member gets a Big. I was lucky enough to have my Emerald Buddy be my Big! I love her so much!

Kappa Phi:
In Kappa Phi we have Bigs and Littles. Usually a Big for a Kappa Phi pledge gets picked within 2 weeks of their pledge initiation and leaves them gifts at every meeting (once a week) until their active initiation where they reveal who they are and give their Littles a paddle. The Littles don't have to return the gift, though I gave my Kappa Phi Big her paddle as a Christmas present.