Hello Lea! I think that the term "graduation trip" means a holiday or "trip" that students would take after graduating, to celebrate their graduation. Also, I think it is a kind of reward that parents offer their children for their hard work put into achieving this. I also think that it is more of an American tradition. South African youngsters take this kind of trip at the end of their secondary (high school) schooling and they call it "Matric Rage" or "Matric Holiday". This is because grade 12 (our final year of high school) used to be called "Matric". I hope that helps! I hope that helps.

I am in the U.S.. It means a young person takes a trip after his or her graduation. It's a celebration for the achievement.