The phrase "uncredited cameo" refers to a brief appearance by a famous person in a movie or TV show, where their name is not mentioned or acknowledged in the credits. Full definition
The film features uncredited cameos by Michael Keaton and Samuel L. Jackson, and was shot in locations in Florida, Louisiana, and Michigan. (rottentomatoes.com)
A late uncredited cameo for one of the biggest stars in the firmament promises panto dastardliness in the sequels to come (no fewer than four more have been slated). (theartsdesk.com)
And if uncredited cameos by the likes of Jerry Lewis, Dean Martin, and Jane Russell aren't enough to entice you, this is the only Road To... movie made in color! (tubitv.com)