From Longman Dictionary of Contemporary Englishwalk-onˈwalk-on noun [countable] 1 (also walk-on part/role)APT a small acting part with no words to say in a play or film, or an actor who has a part like this2 American English someone who plays for a college sports team without having been given a sports scholarship
Examples from the Corpus
walk-on• The ending is a cinematic cop-out using newsreel photo-montage and a walk-on by Nelson Mandela.• Five of their players are walk-ons.• Gardner was a football walk-on at Nebraska, but quit the team in order to concentrate on wrestling.• Down near the basket, Karen is guarding Courtney Kanegae, a five-foot-two freshman walk-on.• Mind, I did rehearse the walk-on, which is quite critical. 