spring recruitment

Spring rush is a LOT more informal. YOU have to be invited to rush by someone in the house, you can't just show up because they already have a list of girls. It's a lot smaller, anywhere between 70-10 girls rushing that house. Each house hosts a few events, like cookie decorating or a dinner, and you would want to go to as many of those as possible. There aren't the rules that exist during fall, so dirty rushing is more common but also girls are allowed to disclose a lot more information if they want.
COB (Continuous Open Bidding) occurs year-round for some houses. Sometimes only winter, sometimes only spring. Spring just happens to be more common, but don't sit around waiting for spring. For instance, last year Gamma Phi did fall formal, informal winter, AND informal spring. Whereas Chi O only did informal somewhere between winter and spring, in addition to fall formal.
Honestly, not one house knows if they have to do informal recruitment. Depends on if/how many girls drop out their houses by the end of fall term. Keep your eyes and ears open and suck up to as many girls in houses that you know, if you want to maximize the amount of houses you see during COB.