A brief history:
NFTY-STR started out as SEFTY, the south eastern federation of temple youth. There was a branch in every region, with its name fitting the region. They changed the name to NFTY, the national federation of temple youth, in order to make it more uniform and get a better sense of group unity. Within NFTY, there are many subdivisions. NFTY-SER (south east region) is the subdivision I was part of...till they change the name again! NFTY-SER was split in two - STR and SAR. STR is the south tropical region and SAR is the south area region.
Every year there are 4 conventions and 2(?) mix & mingles (m&m's). Fall Kallah and Spring Kallah are both from Friday afternoon through Sunday morning and are for either NFTY-STR or NFTY-SAR, not both at the same time. During this time there are many different programs and activities scheduled, and we get to choose wich one to go to. They all relate to Judaism in some way and its really interesting to see the different topics that are brought up during the discussions and how they all relate to Judaism. We stay at other peoples houses for the weekend and there's always a dance on the last night.
Winter Bi-Regionals is 4(?) days and 3(?) nights long, and basically an extended Kallah. The only difference is that both NFTY-STR and NFTY-SAR go to Winter Bi-Regionals and the dance at the end is formal instead of casual.
The m&m's are only one night long, and they include two programs and a dance at the end. If you live an hour or more away from wherever it's being held, you are elligable for housing, though, I never put down housing (even though I'm an hour away) cause there's no guarantee I'll be housed with my friends, and if I can get to their house without requesting housing it works out better for us all:)