"Character cameos" refers to when a well-known character from one story or movie appears briefly in another story or movie as a special guest appearance. Full definition
The game takes its moniker from the cancelled SEGA Neptune console and various SEGA characters cameo in the series. (segadriven.com)
Brief character cameos from Keith Carradine, Louise Fletcher, and Austin Pendleton additionally dot the movie. (austinchronicle.com)
The number of Easter Eggs in Ready Player One could rise into the thousands when all is said and done, filled with more fictional character cameos, video game references and secrets, and superhero tributes than can ever be spotted in theaters. (screenrant.com)