Efficiency is a collectible used for upgrading. (You can use Special:WhatLinksHere/Efficiency to find the list of buildings that use this collectible for upgrade. Last part not working yet...)
This collectible was issued with the limited-time Academia Nuts-themed quests starting on the 12th of October 2012.
You can carry only 10 pieces of Efficiency in your inventory.
This collectible can only be obtained by sending your registered University Students to work at Factories.