What are hidden Easter eggs?

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Tags

1. #traditional
2. #computer
3. #software
4. #feature
5. #program
6. #easter
7. #inside
8. #evoke
9. #secret
10. #usually
11. #found
12. #intentional
13. #hidden
14. #image
15. #message
16. #media
17. #screen
18. #video