sine is the orthogonal projection of the unit circle?

I read that "sine is the orthogonal projection of the unit circle". I know othogonal is another way of saying perpendicular but I still can't quite grasp what is going on here. Can anyone help?

Thanks!

-Andy-

I guess that's a fancy way of saying that sine goes on the y axis and cos on the x axis. Sin 90 =1 etc.