as defined by Encarta® World English Dictionary:
colored hen’s egg for Easter: a hen’s egg that has been dyed, painted, or decorated for Easter, often hidden for children to find in an Easter egg hunt
hidden element of a computer program: a secret message, graphic, animation, or sound effect hidden in a computer program and activated by a specific undocumented sequence of keystrokes. An Easter egg is typically intended as a harmless joke or as a way to display the credits of the program’s development team.
PS – Spring your web experience to life and check out: Google Easter Eggs 2012. (Video)
Oh, and Have a Happy Easter!!!