Efficiency is an enchantment that increases the speed the player mines.
Obtaining
Efficiency V is available only when using an anvil for diamond and stone tools. Wooden, golden and iron tools can get Efficiency V by enchanting.
Usage
The proper tool for a block must be used in order to receive the speed benefit; the enchantment has no effect if the block is mined with the incorrect tool. See Breaking§Speed for details on mining speed.
The speed increase applies to all blocks that drop an item when mined.
Efficiency applied to an axe will increase the chance that the axe may stun a shield, with the base chance being 25% and a 5% increase for each level of efficiency.