In an American school or university, the valedictorian is the student who finished at the very top of the class — the best marks over all the years, not just one exam — and who is therefore given the honour of making the farewell speech at the graduation ceremony. It is a real title, printed in the programme, and American families treat it as a big deal; the runner-up has a name too, 'salutatorian', the one who gives the welcome.

This is worth knowing because it is very American. British schools do not do this, and Taiwan's system is not quite the same either — our 畢業生代表 is chosen partly by grades and partly by other things, and there is no single official ranked winner in the American sense. So when you meet 'valedictorian' in a film or an American news story, understand it as both an academic ranking and a speaking role at once. That double meaning is exactly why the word exists. Say it va-luh-dic-TOR-ee-un, with the stress near the end.