Easter egg
noun
1
a message hidden in a computer program's object code US, 1991.
2
an icon or hidden process on the menu of a DVD that, when selected or followed, leads to hidden features US, 2002.
3
the leg. Rhyming slang UK, 1998.► on the Easter eggbegging, scrounging. Glasgow rhyming slang for ON THE BEG UK: SCOTLAND, 1988