A galvanic anode is the main component of a galvanic
cathodic protection (CP) system used to protect buried or submerged
metal structures from corrosion.
They are made from a metal alloy with a more "active" voltage
(more negative electrochemical potential) than the metal of the
structure. The difference in potential between the two metals means
that the galvanic anode corrodes, so that the anode material is
consumed in preference to the structure.
The loss (or sacrifice) of the anode material gives rise to the
alternative name of sacrificial anode.