Can anyone tell me what this famous music?

its a clical piece. its really elegant and refined and it feels like something that would be played in a ballroom. its very famous. iv heard it in a movie. iv herd it on piano and im pretty sure its played on violin also. im pretty sure a pianist would know what it is. im sure that a lot of pianists know how to play it. but at least give me some possible things it could be. i have to know what it is...