Easter Egg
In the software context, an Easter Egg is a hidden feature or novelty that the programmers have put in their software on purpose. They can be anything including: a list of credits, hidden commands, or even jokes.
According to The Easter Egg Archive, a true Easter Egg must satisfy the following criteria:
- Undocumented, Hidden, and Non-Obvious: A legitimate product feature or an obvious storyline element do not count. Easter Eggs are usually discernable either because they are out of context or they have a personal meaning to the creators.
- Reproducible: Every user must be able to produce the same result. If others can't reproduce it, then it's not an Easter Egg.
- Purposeful Placement: They must have been put there on purpose. Mistakes are bugs, not Easter Eggs.
- Non-Malicious: Easter Eggs are there for fun, not to do damage.