With a waitlist, it is my understanding that you will be considered from a large pool of other students at a later point, where they will decide whether or not they want to accept you. They didn't love you enough to accept you, but didn't hate you enough to reject you. With most alternate lists, they've essentially accepted you, but your ability to attend is contingent upon someone else (who has already been accepted) declining their offer. Some schools say that their waitlists are "unranked (which I honestly don't believe), and at some schools they will tell you what number on the alternate list you are. If you are, lets say, 5th on the list-- you will be offered the position of the fifth person who was originally accepted, but declined their offer.