In software and media, an Easter egg is an intentional hidden message, image, inside joke, or secret feature placed in a work for users to discover on their own.
The name evokes a traditional Easter egg hunt, and the canonical first example is literal enough to have earned it. Warren Robinett, who programmed the Atari 2600 game Adventure, hid a room displaying "Created by Warren Robinett" because Atari's policy at the time was not to credit individual developers. The studio discovered it after release, decided that hunting for hidden rooms was itself a reason to keep playing, and formalized the practice under the name.
Easter eggs have since spread across software, film, and hardware: hidden commands, developer credits, secret levels, cheat codes, and references to other works planted for the audience most likely to catch them. Voice assistants like 📝Siri ship large scripted sets of them, where the payload is personality rather than genuine concealment.
In marketing the mechanic functions as a reward for close attention. A detail only a careful reader finds converts discovery into status, and status into sharing — which is why the egg is usually planted where finding it is plausible but not certain.