If nobody's walked you through the actual structure yet, here it is, because most PNMs go in only knowing "there are rounds" and nothing else.
Round 1 (Open House / Round of Introductions). Short visits, usually 20 to 30 minutes, to every chapter participating. Low stakes, high volume. Think of it as speed dating, the goal is just a pleasant first impression on both sides, nothing more.
Round 2 (Philanthropy Round). Chapters narrow their list, and you narrow yours by ranking who you'd like to see again. Visits get slightly longer, and chapters usually talk about their philanthropy and service work here, hence the name.
Round 3 (Sisterhood Round). Fewer chapters, longer visits, deeper conversation. This round is where chapters show you what daily life in the house actually feels like, and where you start noticing which room feels the least like a performance.
Preference Round (Pref). The final round, one to two chapters max, and the tone shifts completely: quieter, more emotional, more personal. Members speak from the heart about what the chapter means to them. This is covered in its own guide because it deserves one.
Bid Day. You accept a bid (or don't get one at all schools you'd hoped for, which is also covered elsewhere), and it's exactly the celebration everyone's Instagram makes it look like.
Between rounds: you rank your preferences after each one, the matching algorithm uses your rankings and the chapters' rankings together (mutual selection), and you find out which houses invited you back the night before or morning of the next round. The system drops chapters from your schedule as both sides narrow down, not because you did anything wrong, capacity is finite and math happens on both sides.
One honest note: exact round names, number of rounds, and event length vary by school and by NPC council size. A school with 20 chapters runs a longer week than one with 6. Check your specific Panhellenic's schedule the moment it's published, it's the actual source of truth over any generic guide, including this one.