RuneScape Classic Wiki
The main RuneScape Wiki has an article on: Easter egg
The Old School RuneScape Wiki also has an article on Easter egg.

The Easter egg is a discontinued item that was dropped on Easter, 20 April 2002. It has a significantly high value to players because of it's status as an item that could only be obtained on one day.

Consumable status

It can be eaten to restore 12 Hits. Due to its high value, players will usually keep the item in their bank except when trading it to avoid accidentally eating it. This precaution is extremely important because of the item's value and rarity. Other examples of consumable discontinued items are the Pumpkin and Half Full wine jug.