What does the "curve" mean?

What does the “curve” mean and how will it affect my score? I took the SAT II Biology M a couple days ago.

The College Board decides ahead of time how hard the test is in comparison with past SAT II Bio tests. Then, they make the chart that relates your raw score (how many you got right) to your actual score. So, for example, if this was a little easier test, then maybe you could only get one wrong to get a 780. On a harder version, maybe you could get a 780 with two wrong. The “curve” is not the kind of curve you think of that is sometimes used at school. It has nothing to do with how the group of kids did on the test.