The Scramble is used to fill the unfilled positions after the match is complete. Those that did not match are informed that they will have to scramble. The list of unfilled positions and contact phone numbers are released on the ERAS website at 12:00 EST on scramble day. People then begin calling those sites and apply to the unfilled positions, sending their transcripts, CV, letters of recommendation, etc. There is much "scrambling" as calls are returned, things faxed back and forth, etc. There are many busy phone numbers and fax lines. The hope is to find a place that will take you and sign a contract.
Just one addition: "scramble day" happens I think 1-2 days before Match day. So, if you didn't match, you hopefully find a position by match day. And, those who did match will know on scramble day that they matched, although they don't know if they matched at the first or last on their rank list.
So you're told before the scramble that you matched but not where? What's the point of that?
I thougth that, in theory, the scramble went on until every program had its spots filled; and even then there's a second wave to the scramble around july 1st when some interns don't show up and a spot suddenly opens up.
Monday at noon of match week you find out if you matched or not (NRMP sends you an e-mail, or you can find out on their site). Noon on Tuesday the scramble open up and NRMP releases the names of all the unfilled programs. Note that the info on scutwork.com, while correct in the programs that didn't fill isn't entirely accurate. I mean that at noon on Tuesday I had a friend call every radiology program that supposedly didn't match and every single program said they were already filled. How this happens, I have no idea. So, just because you see a program that didn't fill doesn't mean there are really any open slots.
The scramble is really from noon on Tuesday till noon on Thursday for AMG. So those who don't match still get a letter to open up on match day so they don't feel left out (even though those select people know exactly where they're going). There's still spots open after Thursday, in fact there are spots open all year round, but it's no fun to say that there is a scramble 365 days a year.
On Thursday at noon, you open a letter from your medical school (you can wait till one pm EST and find out on the NRMP site, but you find out an hour sooner at your medical school ceremony) and everyone gets excited, TV cameras, nice dinners, etc. They make you wait so that it's a big occasion with everyone together. Opening the envelope is very nerve racking but was fun at the same time.