What is an aluminum anode block?

This is commonly said of aluminum anodes. One is that the insoluble anode such as graphite in electrolysis or electroplating process is called the anode block; The second is to protect a metal from corrosion by connecting it with a metal that is more reductive than the metal. Then the highly reducing metal is called the anode block. Usually what we see is that below the waterline in the hull of a ship, a certain number of blocks of zinc are installed to prevent corrosion of the hull, etc., and this block of zinc or aluminum is called an anode block.