Easter egg

Because eggs were inexpensive in most regions, the practice of decorating Easter eggs crossed all social classes and remained somewhat simple.

I reached the first fork in the tree and there they lay—several melted Easter eggs[…] Quickly I tore open the foil and licked the melted chocolate until there wasn't a trace left on the paper.

an Easter egg that displays the names of the application's development team

For the Best of Bowie DVD release, APl even concealed an Easter egg within a hidden extra.