What is Base Metal?

Legal Definition
A base metal is a common and inexpensive metal, as opposed to a precious metal such as gold or silver. A long-time goal of alchemists was the transmutation of a base (low grade) metal into a precious metal. In numismatics, coins often derived their value from the precious metal content; however, base metals have been also used in coins in the past and today.
-- Wikipedia
Legal Definition
A cheap metal that corrodes when exposed to air or moisture.