Most Helpful Girl
That was a line used by Westley, a farm hand :) Basically Buttercup is this beautiful rich girl who enjoys forcing him to do chores constantly, she doesn't really consider him a person at that point and she tries to torture him through hard work and he remains calm and just replies 'As you wish' to whatever she tells him to do. I mean, literally, it means that he's going to do what she says. But the narrator reveals that what he really meant every time he said 'As you wish' was 'I love you'. It's repeated a lot throughout the book/film, and it's pretty romantic given the various contexts it's used.