Cameo performance

A cameo role or cameo appearance (/ˈkæmioʊ/; often shortened to just cameo) is a brief appearance or voice part of a known person in a work of the performing arts, typically unnamed or appearing as themselves. These roles are generally small, many of them non-speaking ones, and are commonly either appearances in a work in which they hold some special significance (such as actors from an original movie appearing in its remake), or renowned people making uncredited appearances. Short appearances by celebrities, film directors, politicians, athletes, or musicians are common. A crew member of the movie or show playing a minor role can be referred to as a cameo as well, such as Alfred Hitchcock's frequently performed cameos.

Originally "cameo role" meant "a small character part that stands out from the other minor parts". The Oxford English Dictionary connects this with the meaning "a short literary sketch or portrait", which is based on the literal meaning of "cameo", a miniature carving on a gemstone. More recently, "cameo" has come to refer to any short appearances, whether as a character or as oneself, such as the examples below.

Cameos are generally not credited because of their brevity, or a perceived mismatch between the celebrity's stature and the film or TV show in which he or she is appearing. Many are publicity stunts. Others are acknowledgments of an actor's contribution to an earlier work, as in the case of many film adaptations of TV series, or of remakes of earlier films. Others honour artists or celebrities known for work in a particular field.

...
Wikipedia