The first is fraternities. About half of MIT's male population lives in fraternity houses, most of them either along Dorm Row or across the river in Boston. Although MIT guarantees housing to all freshman, and for four years to any student staying within the system, they do not have enough spaces for everybody. Therefore, MIT cannot have a spring fraternity rush, as other schools do. To that end, MIT holds Rush, during which time freshmen can visit all sorts of living groups, and then choose where they would like to live.
The second reason goes across fraternity/dormitory lines. Whether an ILG (Independent Living Group) or a dorm, every living space at MIT is unique. Senior House has a different culture than Alpha Delta Phi fraernity which is different from Baker House which is different than Epsilon Theta which is different from Random Hall. Rather than blindly assign freshmen to dorms which might not be right for them, or even have a freshman dorm to house frosh for the first year, MIT gives students a few days to visit all the different living groups and then choose the option which is right for them.
On the other hand, Rush is an extremely stressful time. You have only a few days to view a dozen dorms and even more ILGs. You need to get around to all the choices to be exposed to them, but at the same time need to spend enough time at the places you really like to get a real sense of what it would be like to live there for four years, and to let the people there get to know you. The time constraints are truly frustrating which makes decisions more difficult. However, that is the system, and we just pick up the pieces. It's not a bad time if you approach it the right way. Rush can be cool. Hey, there's free food almost everywhere!
The answer to this question varies from dorm to dorm.
For us, Rush is a time to present ourselves to freshmen. We hope to meet some cool people who think that we're pretty cool too. It's also a time for us to try to decide what aspects of our lives are the ones that make our home Random Hall and to try to present those qualities to prospective residents as best we can. It's also a time to have fun doing a bunch of wacky things, play with liquid nitrogen, and eat lots of food.
The main idea is that we want people who'll be happy with us and who we'll be happy with, so Rush is a time to come by and give us a shot. See if this is the place you want to crash for a few years.
See you in August,
Aidan